'What' do we call consciousness? 'When' and 'Where' in the brain do conscious states occur, and '... more 'What' do we call consciousness? 'When' and 'Where' in the brain do conscious states occur, and 'How' conscious processing and conscious access to a given content work? In the present paper, we present a non-exhaustive overview of each of these 4 major issues, we provide the reader with a brief description of the major difficulties related to these issues, we highlight the current theoretical points of debate, and we advocate for the explanatory power of the "global workspace" model of consciousness (Baars 1989; Dehaene and Naccache 2001; Dehaene, Changeux et al. 2006) which can accommodate for a fairly large proportion of current experimental findings, and which can be used to reinterpret apparent contradictory findings within a single theoretical framework. Most notably, we emphasize the crucial importance to distinguish genuine neural signatures of conscious access from neural events correlated with consciousness but occurring either before ('upstream') or after ('downstream').
One striking property of perception is that it can be achieved in two seemingly different ways: e... more One striking property of perception is that it can be achieved in two seemingly different ways: either consciously or non-consciously. What distinguishes these two types of processing at the neural level? So far, empirical findings suggest that conscious perception is associated with an increase in activity at the sensory level, the specific involvement of a fronto-parietal network and an increase in long-distance functional connectivity and synchrony within a broad network of areas. We interpret these data in the framework of the global neuronal workspace model which proposes that the neural basis of conscious access is a sudden self-amplifying process leading to a global brain-scale pattern of activity. In contradiction with several theories which assume that there is a continuum of perception, associated with a gradual change in the intensity of brain activation, the model predicts a sharp non-linear transition between non-conscious and conscious processing.
Recent studies have demonstrated that visually cueing attention towards a stimulus location after... more Recent studies have demonstrated that visually cueing attention towards a stimulus location after its disappearance can facilitate visual processing of the target and increase task performance. Here, we tested whether such retro-cueing effects can also occur across different sensory modalities, as cross-modal facilitation has been shown in pre-cueing studies using auditory stimuli prior to the onset of a visual target. in the present study, participants detected low-contrast Gabor patches in a speeded response task. these patches were presented in the left or right visual periphery, preceded or followed by a lateralized and task-irrelevant sound at 4 stimulus-onset asynchronies (SOA; −600 ms, −150 ms, +150 ms, +450 ms). We found that pre-cueing at the −150 ms SOA led to a general increase in detection performance irrespective of the sound's location relative to the target. on top of this temporal effect, sound-cues also had a spatially specific effect, with further improvement when cue and target originated from the same location. Critically, the temporal effect was absent, but the spatial effect was present in the short-SOA retro-cueing condition (+150 ms). Drift-diffusion analysis of the response time distributions allowed us to better characterize the evidenced effects. Overall, our results show that sounds can facilitate visual processing, both pre-and retroactively , indicative of a flexible and multisensory attentional system that underlies our conscious visual experience.
The use of cognitive evoked potentials in EEG is now part of the routine evaluation of non-commun... more The use of cognitive evoked potentials in EEG is now part of the routine evaluation of non-communicating patients with disorders of consciousness in several specialized medical centers around the world. They typically focus on one or two cognitive markers, such as the mismatch negativity or the P3 to global auditory regularity. However it has become clear that none of these markers in isolation is at the same time sufficiently specific and sufficiently sensitive to be taken as the unique gold standard for diagnosing consciousness. A good way forward would be to combine several cognitive markers within the same test to improve evaluation. Furthermore, given the diversity of lesions leading to disorders of consciousness, it is important not only to probe whether a patient is conscious or not, but also to establish a more general and nuanced profile of the residual cognitive capacities of each patient using a combination of markers. In the present study we built a unique EEG protocol that probed 8 dimensions of cognitive processing in a single 1.5 h session. This protocol probed variants of classical markers together with new markers of spatial attention, which has not yet been studied in these patients. The eight dimensions were: (1) own name recognition, (2) temporal attention, (3) spatial attention, (4) detection of spatial incongruence (5) motor planning, and (6,7,8) modulations of these effects by the global context, reflecting higher-level functions. This protocol was tested in 15 healthy control subjects and in 17 patients with various etiologies, among which 13 could be included in the analysis. The results in the control group allowed a validation and a specific description of the cognitive levels probed by each marker. At the single-subject level, this combined protocol allowed assessing the presence of both classical and newly introduced markers for each patient and control, and revealed that the combination of several markers increased diagnostic sensitivity. The presence of a high-level effect in any of the three tested domains distinguished between minimally conscious and vegetative patients, while the presence of low-level effects was similar in both groups. In summary, this study constitutes a validated proof of concept in favor of probing multiple cognitive dimensions to improve the evaluation of non-communicating patients. At a more conceptual level, this EEG tool can help achieve a better understanding of disorders of consciousness by exploring consciousness in its multiple cognitive facets.
In the phenomenon of attentional blink, identical visual stimuli are sometimes fully perceived an... more In the phenomenon of attentional blink, identical visual stimuli are sometimes fully perceived and sometimes not detected at all. This phenomenon thus provides an optimal situation to study the fate of stimuli not consciously perceived and the differences between conscious and nonconscious processing. We correlated behavioral visibility ratings and recordings of event-related potentials to study the temporal dynamics of access to consciousness. Intact early potentials (P1 and N1) were evoked by unseen words, suggesting that these brain events are not the primary correlates of conscious perception. However, we observed a rapid divergence around 270 ms, after which several brain events were evoked solely by seen words. Thus, we suggest that the transition toward access to consciousness relates to the optional triggering of a late wave of activation that spreads through a distributed network of cortical association areas.
Each recording is composed of 3 files: .eeg, .vhdr and .vmrk. The file name includes the particip... more Each recording is composed of 3 files: .eeg, .vhdr and .vmrk. The file name includes the participant number and the session type<br>
A growing body of evidence suggests that conscious perception of a sensory stimulus triggers an a... more A growing body of evidence suggests that conscious perception of a sensory stimulus triggers an all-or-none activity across multiple cortical areas, a phenomenon called ‘ignition’. In contrast, the same stimulus, when undetected, induces only transient activity. In this work, we report a large-scale model of the macaque cortex based on recently quantified structural connectome data. We use this model to simulate a detection task, and demonstrate how a dynamical bifurcation mechanism produces ignition-like events in the model network. The model predicts that feedforward excitatory transmission is primarily mediated by the fast AMPA receptors to ensure rapid signal propagation from sensory to associative areas. In contrast, a greater proportion of the inter-areal feedback projections and local recurrent excitation depend on the slow NMDA receptors, to ensure ignition of distributed frontoparietal activity. Our model predicts, counterintuitively, that fast-responding sensory areas cont...
Does conscious perception occur during initial sensory processing, or does it arise later in a su... more Does conscious perception occur during initial sensory processing, or does it arise later in a supra modal fashion? If conscious access truly depends on supra modal processes, we may be able to induce “asensory perception”, where only the semantic features of a meaningful stimulus are accessed, untied to its sensory attributes. Here we tested this prediction by degrading the low-level sensory representations of visual words in the brain using pattern masking, and subsequently presenting audio words that were either semantically related to the masked word or not. We hypothesized these retrospective semantic cues would reactivate the remaining traces of the masked word in the brain, and induce awareness of any information that was not disrupted by masking. In three separate experiments we show that, when presented with retrospective cues that are semantically related to the masked word, participants are better at detecting the presence of the preceding masked word and naming it, while...
The use of cognitive evoked potentials in EEG is now part of the routine evaluation of non-commun... more The use of cognitive evoked potentials in EEG is now part of the routine evaluation of non-communicating patients with disorders of consciousness in several specialized medical centers around the world. They typically focus on one or two cognitive markers, such as the mismatch negativity or the P3 to global auditory regularity. However it has become clear that none of these markers in isolation is at the same time sufficiently specific and sufficiently sensitive to be taken as the unique gold standard for diagnosing consciousness. A good way forward would be to combine several cognitive markers within the same test to improve evaluation. Furthermore, given the diversity of lesions leading to disorders of consciousness, it is important not only to probe whether a patient is conscious or not, but also to establish a more general and nuanced profile of the residual cognitive capacities of each patient using a combination of markers. In the present study we built a unique EEG protocol that probed 8 dimensions of cognitive processing in a single 1.5 h session. This protocol probed variants of classical markers together with new markers of spatial attention, which has not yet been studied in these patients. The eight dimensions were: (1) own name recognition, (2) temporal attention, (3) spatial attention, (4) detection of spatial incongruence (5) motor planning, and (6,7,8) modulations of these effects by the global context, reflecting higher-level functions. This protocol was tested in 15 healthy control subjects and in 17 patients with various etiologies, among which 13 could be included in the analysis. The results in the control group allowed a validation and a specific description of the cognitive levels probed by each marker. At the single-subject level, this combined protocol allowed assessing the presence of both classical and newly introduced markers for each patient and control, and revealed that the combination of several markers increased diagnostic sensitivity. The presence of a high-level effect in any of the three tested domains distinguished between minimally conscious and vegetative patients, while the presence of low-level effects was similar in both groups. In summary, this study constitutes a validated proof of concept in favor of probing multiple cognitive dimensions to improve the evaluation of non-communicating patients. At a more conceptual level, this EEG tool can help achieve a better understanding of disorders of consciousness by exploring consciousness in its multiple cognitive facets.
Several theories of the neural correlates of consciousness assume that there is a continuum of pe... more Several theories of the neural correlates of consciousness assume that there is a continuum of perception, associated with a gradual change in the intensity of brain activation. But some models, considering reverberation of neural activity as necessary for conscious perception, predict a sharp non-linear transition between unconscious and conscious processing. We asked participants to evaluate the visibility of target words on a continuous scale during the attentional blink, which is known to impede explicit reports. Participants used this continuous scale in an all-or-none fashion : targets were either identified as well as targets presented outside the blink period or not detected at all. We suggest that a stochastic non-linear bifurcation in neural activity underlies the all-or-none perception observed during the attentional blink.
Objective: Probing consciousness in noncommunicating patients is a major medical and neuroscienti... more Objective: Probing consciousness in noncommunicating patients is a major medical and neuroscientific challenge. While standardized and expert behavioral assessment of patients constitutes a mandatory step, this clinical evaluation stage is often difficult and doubtful, and calls for complementary measures which may overcome its inherent limitations. Several functional brain imaging methods are currently being developed within this perspective, including fMRI and cognitive event-related potentials (ERPs). We recently designed an original rule extraction ERP test that is positive only in subjects who are conscious of the long-term regularity of auditory stimuli. In the present work, we report the results of this test in a population of 22 patients who met clinical criteria for vegetative state. We identified 2 patients showing this neural signature of consciousness. Interestingly, these 2 patients showed unequivocal clinical signs of consciousness within the 3 to 4 days following ERP recording. Taken together, these results strengthen the relevance of bedside neurophysiological tools to improve diagnosis of consciousness in noncommunicating patients. Neurology ® 2011; 77:264-268 GLOSSARY CRS-R ϭ Coma Recovery Scale-Revised; ERP ϭ event-related potential; MCS ϭ minimally conscious state; VS ϭ vegetative state.
One striking property of perception is that it can be achieved in two seemingly different ways: e... more One striking property of perception is that it can be achieved in two seemingly different ways: either consciously or non-consciously. What distinguishes these two types of processing at the neural level? So far, empirical findings suggest that conscious perception is associated with an increase in activity at the sensory level, the specific involvement of a fronto-parietal network and an increase in long-distance functional connectivity and synchrony within a broad network of areas. We interpret these data in the framework of the global neuronal workspace model which proposes that the neural basis of conscious access is a sudden self-amplifying process leading to a global brain-scale pattern of activity. In contradiction with several theories which assume that there is a continuum of perception, associated with a gradual change in the intensity of brain activation, the model predicts a sharp non-linear transition between non-conscious and conscious processing.
Right-hemisphere lesions often lead to severe disorders in spatial awareness and behavior, such a... more Right-hemisphere lesions often lead to severe disorders in spatial awareness and behavior, such as left hemispatial neglect. Neglect involves not only pathological biases in attention and exploration, but also deficits in internal representations of space and spatial working memory. Here we designed a new paradigm to test whether one potential component may involve a failure to maintain an updated representation of visual locations across delays when a gaze-shift intervenes. Right-hemisphere patients with varying severity of left spatial neglect had to encode a single target location and retain it across an interval of 2 or 3 seconds, during which the target was transiently removed, before a subsequent probe appeared for a same/different location judgment. During the delay, gaze could have to shift to either side of the remembered location, or no gazeshift was required. Patients showed a dramatic loss of memory for target location after shifting gaze to its right (towards their 'intact' ipsilesional side), but not after leftward gaze-shifts. Such impairment arose even when the target initially appeared in the right visual field, before being updated leftward due to right gaze; and even when gaze returned to screen center before the memory probe was presented. These findings indicate that location information may be permanently degraded when the target has to be remapped leftward in gaze-centric representations. Across patients, the location-memory deficit induced by rightward gaze-shifts correlated with left neglect severity on several clinical tests. This paradoxical memory deficit, with worse performance following gaze-shifts to the 'intact' side of space, may reflect losses in gazecentric representations of space that normally remap a remembered location dynamically relative to current gaze. Right gaze-shifts may remap remembered locations leftward, into damaged representations; whereas left gaze-shifts will require remapping rightward, into intact representations. Our findings accord with physiological data on normal remapping mechanisms in the primate brain, but demonstrate for the first time their impact on perceptual spatial memory when damaged, while providing new insights into possible components that may contribute to the neglect syndrome.
Of the many brain events evoked by a visual stimulus, which are specifically associated with cons... more Of the many brain events evoked by a visual stimulus, which are specifically associated with conscious perception, and which merely reflect non-conscious processing? Several recent neuroimaging studies have contrasted conscious ...
An outstanding challenge for consciousness research is to characterize the neural signature of co... more An outstanding challenge for consciousness research is to characterize the neural signature of conscious access independently of any decisional processes. Here we present a model-based approach that uses inter-trial variability to identify the brain dynamics associated with stimulus processing. We demonstrate that, even in the absence of any task or behavior, the electroencephalographic response to auditory stimuli shows bifurcation dynamics around 250–300 milliseconds post-stimulus. Namely, the same stimulus gives rise to late sustained activity on some trials, and not on others. This late neural activity is predictive of task-related reports, and also of reports of conscious contents that are randomly sampled during task-free listening. Source localization further suggests that task-free conscious access recruits the same neural networks as those associated with explicit report, except for frontal executive components. Studying brain dynamics through variability could thus play a ...
Despite the tangible progress in psychological and cognitive sciences over the last several years... more Despite the tangible progress in psychological and cognitive sciences over the last several years, these disciplines still trail other more mature sciences in identifying the most important questions that need to be solved. Reaching such consensus could lead to greater synergy across different laboratories, faster progress, and increased focus on solving important problems rather than pursuing isolated, niche efforts. Here, 26 researchers from the field of visual metacognition reached consensus on four long-term and two medium-term common goals. We describe the process that we followed, the goals themselves, and our plans for accomplishing these goals. If this effort proves successful within the next few years, such consensus-building around common goals could be adopted more widely in psychological science.
'What' do we call consciousness? 'When' and 'Where' in the brain do conscious states occur, and '... more 'What' do we call consciousness? 'When' and 'Where' in the brain do conscious states occur, and 'How' conscious processing and conscious access to a given content work? In the present paper, we present a non-exhaustive overview of each of these 4 major issues, we provide the reader with a brief description of the major difficulties related to these issues, we highlight the current theoretical points of debate, and we advocate for the explanatory power of the "global workspace" model of consciousness (Baars 1989; Dehaene and Naccache 2001; Dehaene, Changeux et al. 2006) which can accommodate for a fairly large proportion of current experimental findings, and which can be used to reinterpret apparent contradictory findings within a single theoretical framework. Most notably, we emphasize the crucial importance to distinguish genuine neural signatures of conscious access from neural events correlated with consciousness but occurring either before ('upstream') or after ('downstream').
One striking property of perception is that it can be achieved in two seemingly different ways: e... more One striking property of perception is that it can be achieved in two seemingly different ways: either consciously or non-consciously. What distinguishes these two types of processing at the neural level? So far, empirical findings suggest that conscious perception is associated with an increase in activity at the sensory level, the specific involvement of a fronto-parietal network and an increase in long-distance functional connectivity and synchrony within a broad network of areas. We interpret these data in the framework of the global neuronal workspace model which proposes that the neural basis of conscious access is a sudden self-amplifying process leading to a global brain-scale pattern of activity. In contradiction with several theories which assume that there is a continuum of perception, associated with a gradual change in the intensity of brain activation, the model predicts a sharp non-linear transition between non-conscious and conscious processing.
Recent studies have demonstrated that visually cueing attention towards a stimulus location after... more Recent studies have demonstrated that visually cueing attention towards a stimulus location after its disappearance can facilitate visual processing of the target and increase task performance. Here, we tested whether such retro-cueing effects can also occur across different sensory modalities, as cross-modal facilitation has been shown in pre-cueing studies using auditory stimuli prior to the onset of a visual target. in the present study, participants detected low-contrast Gabor patches in a speeded response task. these patches were presented in the left or right visual periphery, preceded or followed by a lateralized and task-irrelevant sound at 4 stimulus-onset asynchronies (SOA; −600 ms, −150 ms, +150 ms, +450 ms). We found that pre-cueing at the −150 ms SOA led to a general increase in detection performance irrespective of the sound's location relative to the target. on top of this temporal effect, sound-cues also had a spatially specific effect, with further improvement when cue and target originated from the same location. Critically, the temporal effect was absent, but the spatial effect was present in the short-SOA retro-cueing condition (+150 ms). Drift-diffusion analysis of the response time distributions allowed us to better characterize the evidenced effects. Overall, our results show that sounds can facilitate visual processing, both pre-and retroactively , indicative of a flexible and multisensory attentional system that underlies our conscious visual experience.
The use of cognitive evoked potentials in EEG is now part of the routine evaluation of non-commun... more The use of cognitive evoked potentials in EEG is now part of the routine evaluation of non-communicating patients with disorders of consciousness in several specialized medical centers around the world. They typically focus on one or two cognitive markers, such as the mismatch negativity or the P3 to global auditory regularity. However it has become clear that none of these markers in isolation is at the same time sufficiently specific and sufficiently sensitive to be taken as the unique gold standard for diagnosing consciousness. A good way forward would be to combine several cognitive markers within the same test to improve evaluation. Furthermore, given the diversity of lesions leading to disorders of consciousness, it is important not only to probe whether a patient is conscious or not, but also to establish a more general and nuanced profile of the residual cognitive capacities of each patient using a combination of markers. In the present study we built a unique EEG protocol that probed 8 dimensions of cognitive processing in a single 1.5 h session. This protocol probed variants of classical markers together with new markers of spatial attention, which has not yet been studied in these patients. The eight dimensions were: (1) own name recognition, (2) temporal attention, (3) spatial attention, (4) detection of spatial incongruence (5) motor planning, and (6,7,8) modulations of these effects by the global context, reflecting higher-level functions. This protocol was tested in 15 healthy control subjects and in 17 patients with various etiologies, among which 13 could be included in the analysis. The results in the control group allowed a validation and a specific description of the cognitive levels probed by each marker. At the single-subject level, this combined protocol allowed assessing the presence of both classical and newly introduced markers for each patient and control, and revealed that the combination of several markers increased diagnostic sensitivity. The presence of a high-level effect in any of the three tested domains distinguished between minimally conscious and vegetative patients, while the presence of low-level effects was similar in both groups. In summary, this study constitutes a validated proof of concept in favor of probing multiple cognitive dimensions to improve the evaluation of non-communicating patients. At a more conceptual level, this EEG tool can help achieve a better understanding of disorders of consciousness by exploring consciousness in its multiple cognitive facets.
In the phenomenon of attentional blink, identical visual stimuli are sometimes fully perceived an... more In the phenomenon of attentional blink, identical visual stimuli are sometimes fully perceived and sometimes not detected at all. This phenomenon thus provides an optimal situation to study the fate of stimuli not consciously perceived and the differences between conscious and nonconscious processing. We correlated behavioral visibility ratings and recordings of event-related potentials to study the temporal dynamics of access to consciousness. Intact early potentials (P1 and N1) were evoked by unseen words, suggesting that these brain events are not the primary correlates of conscious perception. However, we observed a rapid divergence around 270 ms, after which several brain events were evoked solely by seen words. Thus, we suggest that the transition toward access to consciousness relates to the optional triggering of a late wave of activation that spreads through a distributed network of cortical association areas.
Each recording is composed of 3 files: .eeg, .vhdr and .vmrk. The file name includes the particip... more Each recording is composed of 3 files: .eeg, .vhdr and .vmrk. The file name includes the participant number and the session type<br>
A growing body of evidence suggests that conscious perception of a sensory stimulus triggers an a... more A growing body of evidence suggests that conscious perception of a sensory stimulus triggers an all-or-none activity across multiple cortical areas, a phenomenon called ‘ignition’. In contrast, the same stimulus, when undetected, induces only transient activity. In this work, we report a large-scale model of the macaque cortex based on recently quantified structural connectome data. We use this model to simulate a detection task, and demonstrate how a dynamical bifurcation mechanism produces ignition-like events in the model network. The model predicts that feedforward excitatory transmission is primarily mediated by the fast AMPA receptors to ensure rapid signal propagation from sensory to associative areas. In contrast, a greater proportion of the inter-areal feedback projections and local recurrent excitation depend on the slow NMDA receptors, to ensure ignition of distributed frontoparietal activity. Our model predicts, counterintuitively, that fast-responding sensory areas cont...
Does conscious perception occur during initial sensory processing, or does it arise later in a su... more Does conscious perception occur during initial sensory processing, or does it arise later in a supra modal fashion? If conscious access truly depends on supra modal processes, we may be able to induce “asensory perception”, where only the semantic features of a meaningful stimulus are accessed, untied to its sensory attributes. Here we tested this prediction by degrading the low-level sensory representations of visual words in the brain using pattern masking, and subsequently presenting audio words that were either semantically related to the masked word or not. We hypothesized these retrospective semantic cues would reactivate the remaining traces of the masked word in the brain, and induce awareness of any information that was not disrupted by masking. In three separate experiments we show that, when presented with retrospective cues that are semantically related to the masked word, participants are better at detecting the presence of the preceding masked word and naming it, while...
The use of cognitive evoked potentials in EEG is now part of the routine evaluation of non-commun... more The use of cognitive evoked potentials in EEG is now part of the routine evaluation of non-communicating patients with disorders of consciousness in several specialized medical centers around the world. They typically focus on one or two cognitive markers, such as the mismatch negativity or the P3 to global auditory regularity. However it has become clear that none of these markers in isolation is at the same time sufficiently specific and sufficiently sensitive to be taken as the unique gold standard for diagnosing consciousness. A good way forward would be to combine several cognitive markers within the same test to improve evaluation. Furthermore, given the diversity of lesions leading to disorders of consciousness, it is important not only to probe whether a patient is conscious or not, but also to establish a more general and nuanced profile of the residual cognitive capacities of each patient using a combination of markers. In the present study we built a unique EEG protocol that probed 8 dimensions of cognitive processing in a single 1.5 h session. This protocol probed variants of classical markers together with new markers of spatial attention, which has not yet been studied in these patients. The eight dimensions were: (1) own name recognition, (2) temporal attention, (3) spatial attention, (4) detection of spatial incongruence (5) motor planning, and (6,7,8) modulations of these effects by the global context, reflecting higher-level functions. This protocol was tested in 15 healthy control subjects and in 17 patients with various etiologies, among which 13 could be included in the analysis. The results in the control group allowed a validation and a specific description of the cognitive levels probed by each marker. At the single-subject level, this combined protocol allowed assessing the presence of both classical and newly introduced markers for each patient and control, and revealed that the combination of several markers increased diagnostic sensitivity. The presence of a high-level effect in any of the three tested domains distinguished between minimally conscious and vegetative patients, while the presence of low-level effects was similar in both groups. In summary, this study constitutes a validated proof of concept in favor of probing multiple cognitive dimensions to improve the evaluation of non-communicating patients. At a more conceptual level, this EEG tool can help achieve a better understanding of disorders of consciousness by exploring consciousness in its multiple cognitive facets.
Several theories of the neural correlates of consciousness assume that there is a continuum of pe... more Several theories of the neural correlates of consciousness assume that there is a continuum of perception, associated with a gradual change in the intensity of brain activation. But some models, considering reverberation of neural activity as necessary for conscious perception, predict a sharp non-linear transition between unconscious and conscious processing. We asked participants to evaluate the visibility of target words on a continuous scale during the attentional blink, which is known to impede explicit reports. Participants used this continuous scale in an all-or-none fashion : targets were either identified as well as targets presented outside the blink period or not detected at all. We suggest that a stochastic non-linear bifurcation in neural activity underlies the all-or-none perception observed during the attentional blink.
Objective: Probing consciousness in noncommunicating patients is a major medical and neuroscienti... more Objective: Probing consciousness in noncommunicating patients is a major medical and neuroscientific challenge. While standardized and expert behavioral assessment of patients constitutes a mandatory step, this clinical evaluation stage is often difficult and doubtful, and calls for complementary measures which may overcome its inherent limitations. Several functional brain imaging methods are currently being developed within this perspective, including fMRI and cognitive event-related potentials (ERPs). We recently designed an original rule extraction ERP test that is positive only in subjects who are conscious of the long-term regularity of auditory stimuli. In the present work, we report the results of this test in a population of 22 patients who met clinical criteria for vegetative state. We identified 2 patients showing this neural signature of consciousness. Interestingly, these 2 patients showed unequivocal clinical signs of consciousness within the 3 to 4 days following ERP recording. Taken together, these results strengthen the relevance of bedside neurophysiological tools to improve diagnosis of consciousness in noncommunicating patients. Neurology ® 2011; 77:264-268 GLOSSARY CRS-R ϭ Coma Recovery Scale-Revised; ERP ϭ event-related potential; MCS ϭ minimally conscious state; VS ϭ vegetative state.
One striking property of perception is that it can be achieved in two seemingly different ways: e... more One striking property of perception is that it can be achieved in two seemingly different ways: either consciously or non-consciously. What distinguishes these two types of processing at the neural level? So far, empirical findings suggest that conscious perception is associated with an increase in activity at the sensory level, the specific involvement of a fronto-parietal network and an increase in long-distance functional connectivity and synchrony within a broad network of areas. We interpret these data in the framework of the global neuronal workspace model which proposes that the neural basis of conscious access is a sudden self-amplifying process leading to a global brain-scale pattern of activity. In contradiction with several theories which assume that there is a continuum of perception, associated with a gradual change in the intensity of brain activation, the model predicts a sharp non-linear transition between non-conscious and conscious processing.
Right-hemisphere lesions often lead to severe disorders in spatial awareness and behavior, such a... more Right-hemisphere lesions often lead to severe disorders in spatial awareness and behavior, such as left hemispatial neglect. Neglect involves not only pathological biases in attention and exploration, but also deficits in internal representations of space and spatial working memory. Here we designed a new paradigm to test whether one potential component may involve a failure to maintain an updated representation of visual locations across delays when a gaze-shift intervenes. Right-hemisphere patients with varying severity of left spatial neglect had to encode a single target location and retain it across an interval of 2 or 3 seconds, during which the target was transiently removed, before a subsequent probe appeared for a same/different location judgment. During the delay, gaze could have to shift to either side of the remembered location, or no gazeshift was required. Patients showed a dramatic loss of memory for target location after shifting gaze to its right (towards their 'intact' ipsilesional side), but not after leftward gaze-shifts. Such impairment arose even when the target initially appeared in the right visual field, before being updated leftward due to right gaze; and even when gaze returned to screen center before the memory probe was presented. These findings indicate that location information may be permanently degraded when the target has to be remapped leftward in gaze-centric representations. Across patients, the location-memory deficit induced by rightward gaze-shifts correlated with left neglect severity on several clinical tests. This paradoxical memory deficit, with worse performance following gaze-shifts to the 'intact' side of space, may reflect losses in gazecentric representations of space that normally remap a remembered location dynamically relative to current gaze. Right gaze-shifts may remap remembered locations leftward, into damaged representations; whereas left gaze-shifts will require remapping rightward, into intact representations. Our findings accord with physiological data on normal remapping mechanisms in the primate brain, but demonstrate for the first time their impact on perceptual spatial memory when damaged, while providing new insights into possible components that may contribute to the neglect syndrome.
Of the many brain events evoked by a visual stimulus, which are specifically associated with cons... more Of the many brain events evoked by a visual stimulus, which are specifically associated with conscious perception, and which merely reflect non-conscious processing? Several recent neuroimaging studies have contrasted conscious ...
An outstanding challenge for consciousness research is to characterize the neural signature of co... more An outstanding challenge for consciousness research is to characterize the neural signature of conscious access independently of any decisional processes. Here we present a model-based approach that uses inter-trial variability to identify the brain dynamics associated with stimulus processing. We demonstrate that, even in the absence of any task or behavior, the electroencephalographic response to auditory stimuli shows bifurcation dynamics around 250–300 milliseconds post-stimulus. Namely, the same stimulus gives rise to late sustained activity on some trials, and not on others. This late neural activity is predictive of task-related reports, and also of reports of conscious contents that are randomly sampled during task-free listening. Source localization further suggests that task-free conscious access recruits the same neural networks as those associated with explicit report, except for frontal executive components. Studying brain dynamics through variability could thus play a ...
Despite the tangible progress in psychological and cognitive sciences over the last several years... more Despite the tangible progress in psychological and cognitive sciences over the last several years, these disciplines still trail other more mature sciences in identifying the most important questions that need to be solved. Reaching such consensus could lead to greater synergy across different laboratories, faster progress, and increased focus on solving important problems rather than pursuing isolated, niche efforts. Here, 26 researchers from the field of visual metacognition reached consensus on four long-term and two medium-term common goals. We describe the process that we followed, the goals themselves, and our plans for accomplishing these goals. If this effort proves successful within the next few years, such consensus-building around common goals could be adopted more widely in psychological science.
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Papers by Claire Sergent