It has been suggested that cocaine addiction affects the engagement of the frontoparietal network... more It has been suggested that cocaine addiction affects the engagement of the frontoparietal networks in executive functions, such as attention and working memory. Thus, our objective was to investigate brain differences between cocaine-dependent subjects and healthy controls during the performance of a verbal working memory task. Nineteen comparison men and nineteen cocaine-dependent men performed a 2-back task. Data were acquired on a 1.5-T Siemens Avanto. Image processing and statistical analyses were carried out using SPM5; Biological Parametric Mapping (BPM) was used for further morphometric and correlation analyses. No performance differences were found between groups. However, the dorsal part of the right inferior parietal cortex (BA 40) was less activated in the cocaine-dependent group. Cocaine patients did not overactive any brain area when compared with controls. Our results show reduced activation in the brain areas related to the attention system in cocaine-dependent men while performing a verbal working memory task. Chronic cocaine use may affect the attentional system in the right parietal lobe, making patients more prone to attentional deficits.► Chronic cocaine use may affect the attentional system in the right parietal lobe. ► Equal groups' performance can improve the interpretation of functional differences. ► The control of variability in gray matter increase the size of functional results.
The Reinforcement Sensitivity Theory proposes that a neurobiological system, the Behavioral Activ... more The Reinforcement Sensitivity Theory proposes that a neurobiological system, the Behavioral Activation System, defines individual differences on the subject’s sensitivity and reactivity to appetitive stimuli associated with mesocorticolimbic structures, while this system does not mediate aversive stimulus processing. However, Jeffrey A. Gray’s model also predicts the system’s antagonism between this appetitive system and another aversive stimulus sensitive system, the Behavioral Inhibitory System/Fight-Flight-Freeze System, mostly associated with limbic structures. Therefore, direct modulation of brain activation during appetitive stimulus processing should be expected from the Behavioral Activation System, while inverse modulation during aversive stimulus processing may be expected to reflect the system’s antagonism. Using the Sensitivity to Reward scale of the SPSR questionnaire to assess individual differences in the activity of the reward system, we present different behavioral and neuroimaging data to illustrate our view. The first experiment was based on a simple letter-judgment task while viewing erotic and aversive pictures selected from the International Affective Picture System. A second experiment employed a task performed by participants to detect infrequent aversive (i.e., stop) signals when responding to reward. The results from these studies were consistent with the idea that Behavioral Activation System-related personality traits mediate the brain activation associated with appetitive stimulus processing in reward-related areas, while it also showed its antagonism to aversive systems through a negative mediation on the limbic cortex activation. To conclude, sensitivity to reward may be understood as a form of impulsivity related to both better appetitive learning and poorer aversive learning.
Recent research has examined anxiety and hyperactivity in the amygdala and the anterior hippocamp... more Recent research has examined anxiety and hyperactivity in the amygdala and the anterior hippocampus while processing aversive stimuli. In order to determine whether these functional differences have a structural basis, optimized voxel-based morphometry was used to study the relationship between gray matter concentration in the brain and scores on a Behavioral Inhibition System measure (the Sensitivity to Punishment scale) in a sample of 63 male undergraduates. Results showed a positive correlation between Sensitivity to Punishment scores and gray matter volume in the amygdala and the hippocampal formation, that is, in areas that Gray, J.A., and McNaughton, N.J. (2000). The neuropsychology of anxiety. Oxford: Oxford Medical Publications. associated with the Behavioral Inhibition System.
A semi-empirical method to determine radionuclide concentrations in large environmental samples w... more A semi-empirical method to determine radionuclide concentrations in large environmental samples without the use of reference material and avoiding the typical complexity of Monte-Carlo codes is proposed. The calculation of full-energy peak efficiencies was carried out from a relative efficiency curve (obtained from the gamma spectra data), and the geometric (simulated by Monte-Carlo), absorption, sample and intrinsic efficiencies for energies between 130 and 3000 keV. The absorption and sample efficiencies were determined from the mass absorption coefficients, whereas the intrinsic efficiency was approximated by an empirical function. The deviations between calculated and experimental efficiencies for a reference material in most cases are less than 10%. Radionuclide activities in marine sediment samples calculated by the proposed method and by the experimental comparative method were not significantly different. This new method can be used for routine environmental monitoring when uncertainties up to 10% are acceptable.
We used fMRI to study brain activity associated with the performance of a pre-learned sequence of... more We used fMRI to study brain activity associated with the performance of a pre-learned sequence of complex movements of the hand-made unimanually in a group of 13 Parkinson's disease patients and a group of 11 control volunteers. Patients were scanned “off” medication. In controls, sequential movements led to the activation of bilateral sensorimotor and premotor cortex, bilateral inferior parietal cortex, supplementary motor area, bilateral putamen and globus pallidus, and the left ventral lateral nucleus of the thalamus. Sequential movements in the Parkinson's disease group were associated with a similar pattern of activation, although relative decrease of activation in striatum and thalamic areas was observed. Patients in comparison with controls showed a hyperactivation in ipsilateral premotor areas and a hypoactivation in structures of the frontostriatal motor loop. Furthermore, patient scores in the motor scale of the UPDRS correlated positively with the activation thalamus and motor cortical areas during the sequential motor task. We concluded that in Parkinson's disease there is a compensatory mechanism of the dopamine deficit in frontostriatal motor circuits that increases participation in the execution of motor tasks of parietal–lateral premotor circuits.
Using optimized voxel-based morphometry, we studied the relationship between gray matter volume i... more Using optimized voxel-based morphometry, we studied the relationship between gray matter volume in brain areas associated with reward and scores on a behavioral activation system measure (the Sensitivity to Reward scale) in a sample of 50 male undergraduates. Voxel-based morphometry analysis revealed a negative correlation between Sensitivity to Reward scores and gray matter volume in the dorsal striatum and prefrontal cortex. Results indicate that a reduced volume in the striatum might be associated with enhanced reward sensitivity and deficits in inhibitory control.
Cortical reorganization in multiple sclerosis (MS) is defined as a compensatory mechanism which r... more Cortical reorganization in multiple sclerosis (MS) is defined as a compensatory mechanism which requires MS patients to overactivate specific brain areas in order to perform the task as controls. To investigate this process with the Paced Auditory Serial Addition Test (PASAT) task, we selected 15 MS patients who performed the PASAT task within-normal limits and 10 healthy controls. Once selected, we used functional magnetic resonance imaging (fMRI) to investigate brain areas involved in PASAT performance in both groups. Results showed that the task activated the left frontal (BA6 and 9) and parietal cortex (BA7 and 40) in both groups, but MS patients showed a stronger activation in the left prefrontal cortex (BA9, 44 and 45) when compared with controls. These results confirmed those obtained post hoc by Audoin et al. [Audoin, B., Ibarrola, D., Ranjeva, J.P., Confort-Gouny, S., Malikova, I., Ali-Chérif, A.M., Pelletier, J., Cozzone, P., et al., 2003. Compensatory cortical activation observed by fMRI during cognitive task at the earliest stage of MS. Hum. Brain Mapp. 20, 51–58], and we interpreted this as showing true cortical reorganization.
It has been suggested that cocaine addiction affects the engagement of the frontoparietal network... more It has been suggested that cocaine addiction affects the engagement of the frontoparietal networks in executive functions, such as attention and working memory. Thus, our objective was to investigate brain differences between cocaine-dependent subjects and healthy controls during the performance of a verbal working memory task. Nineteen comparison men and nineteen cocaine-dependent men performed a 2-back task. Data were acquired on a 1.5-T Siemens Avanto. Image processing and statistical analyses were carried out using SPM5; Biological Parametric Mapping (BPM) was used for further morphometric and correlation analyses. No performance differences were found between groups. However, the dorsal part of the right inferior parietal cortex (BA 40) was less activated in the cocaine-dependent group. Cocaine patients did not overactive any brain area when compared with controls. Our results show reduced activation in the brain areas related to the attention system in cocaine-dependent men while performing a verbal working memory task. Chronic cocaine use may affect the attentional system in the right parietal lobe, making patients more prone to attentional deficits.► Chronic cocaine use may affect the attentional system in the right parietal lobe. ► Equal groups' performance can improve the interpretation of functional differences. ► The control of variability in gray matter increase the size of functional results.
The Reinforcement Sensitivity Theory proposes that a neurobiological system, the Behavioral Activ... more The Reinforcement Sensitivity Theory proposes that a neurobiological system, the Behavioral Activation System, defines individual differences on the subject’s sensitivity and reactivity to appetitive stimuli associated with mesocorticolimbic structures, while this system does not mediate aversive stimulus processing. However, Jeffrey A. Gray’s model also predicts the system’s antagonism between this appetitive system and another aversive stimulus sensitive system, the Behavioral Inhibitory System/Fight-Flight-Freeze System, mostly associated with limbic structures. Therefore, direct modulation of brain activation during appetitive stimulus processing should be expected from the Behavioral Activation System, while inverse modulation during aversive stimulus processing may be expected to reflect the system’s antagonism. Using the Sensitivity to Reward scale of the SPSR questionnaire to assess individual differences in the activity of the reward system, we present different behavioral and neuroimaging data to illustrate our view. The first experiment was based on a simple letter-judgment task while viewing erotic and aversive pictures selected from the International Affective Picture System. A second experiment employed a task performed by participants to detect infrequent aversive (i.e., stop) signals when responding to reward. The results from these studies were consistent with the idea that Behavioral Activation System-related personality traits mediate the brain activation associated with appetitive stimulus processing in reward-related areas, while it also showed its antagonism to aversive systems through a negative mediation on the limbic cortex activation. To conclude, sensitivity to reward may be understood as a form of impulsivity related to both better appetitive learning and poorer aversive learning.
Recent research has examined anxiety and hyperactivity in the amygdala and the anterior hippocamp... more Recent research has examined anxiety and hyperactivity in the amygdala and the anterior hippocampus while processing aversive stimuli. In order to determine whether these functional differences have a structural basis, optimized voxel-based morphometry was used to study the relationship between gray matter concentration in the brain and scores on a Behavioral Inhibition System measure (the Sensitivity to Punishment scale) in a sample of 63 male undergraduates. Results showed a positive correlation between Sensitivity to Punishment scores and gray matter volume in the amygdala and the hippocampal formation, that is, in areas that Gray, J.A., and McNaughton, N.J. (2000). The neuropsychology of anxiety. Oxford: Oxford Medical Publications. associated with the Behavioral Inhibition System.
A semi-empirical method to determine radionuclide concentrations in large environmental samples w... more A semi-empirical method to determine radionuclide concentrations in large environmental samples without the use of reference material and avoiding the typical complexity of Monte-Carlo codes is proposed. The calculation of full-energy peak efficiencies was carried out from a relative efficiency curve (obtained from the gamma spectra data), and the geometric (simulated by Monte-Carlo), absorption, sample and intrinsic efficiencies for energies between 130 and 3000 keV. The absorption and sample efficiencies were determined from the mass absorption coefficients, whereas the intrinsic efficiency was approximated by an empirical function. The deviations between calculated and experimental efficiencies for a reference material in most cases are less than 10%. Radionuclide activities in marine sediment samples calculated by the proposed method and by the experimental comparative method were not significantly different. This new method can be used for routine environmental monitoring when uncertainties up to 10% are acceptable.
We used fMRI to study brain activity associated with the performance of a pre-learned sequence of... more We used fMRI to study brain activity associated with the performance of a pre-learned sequence of complex movements of the hand-made unimanually in a group of 13 Parkinson's disease patients and a group of 11 control volunteers. Patients were scanned “off” medication. In controls, sequential movements led to the activation of bilateral sensorimotor and premotor cortex, bilateral inferior parietal cortex, supplementary motor area, bilateral putamen and globus pallidus, and the left ventral lateral nucleus of the thalamus. Sequential movements in the Parkinson's disease group were associated with a similar pattern of activation, although relative decrease of activation in striatum and thalamic areas was observed. Patients in comparison with controls showed a hyperactivation in ipsilateral premotor areas and a hypoactivation in structures of the frontostriatal motor loop. Furthermore, patient scores in the motor scale of the UPDRS correlated positively with the activation thalamus and motor cortical areas during the sequential motor task. We concluded that in Parkinson's disease there is a compensatory mechanism of the dopamine deficit in frontostriatal motor circuits that increases participation in the execution of motor tasks of parietal–lateral premotor circuits.
Using optimized voxel-based morphometry, we studied the relationship between gray matter volume i... more Using optimized voxel-based morphometry, we studied the relationship between gray matter volume in brain areas associated with reward and scores on a behavioral activation system measure (the Sensitivity to Reward scale) in a sample of 50 male undergraduates. Voxel-based morphometry analysis revealed a negative correlation between Sensitivity to Reward scores and gray matter volume in the dorsal striatum and prefrontal cortex. Results indicate that a reduced volume in the striatum might be associated with enhanced reward sensitivity and deficits in inhibitory control.
Cortical reorganization in multiple sclerosis (MS) is defined as a compensatory mechanism which r... more Cortical reorganization in multiple sclerosis (MS) is defined as a compensatory mechanism which requires MS patients to overactivate specific brain areas in order to perform the task as controls. To investigate this process with the Paced Auditory Serial Addition Test (PASAT) task, we selected 15 MS patients who performed the PASAT task within-normal limits and 10 healthy controls. Once selected, we used functional magnetic resonance imaging (fMRI) to investigate brain areas involved in PASAT performance in both groups. Results showed that the task activated the left frontal (BA6 and 9) and parietal cortex (BA7 and 40) in both groups, but MS patients showed a stronger activation in the left prefrontal cortex (BA9, 44 and 45) when compared with controls. These results confirmed those obtained post hoc by Audoin et al. [Audoin, B., Ibarrola, D., Ranjeva, J.P., Confort-Gouny, S., Malikova, I., Ali-Chérif, A.M., Pelletier, J., Cozzone, P., et al., 2003. Compensatory cortical activation observed by fMRI during cognitive task at the earliest stage of MS. Hum. Brain Mapp. 20, 51–58], and we interpreted this as showing true cortical reorganization.
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Papers by Alfonso Barros