Amblyopia is a neurodevelopmental disorder of vision that occurs when the visual cortex receives ... more Amblyopia is a neurodevelopmental disorder of vision that occurs when the visual cortex receives decorrelated inputs from the two eyes during an early critical period of development. Amblyopic eyes are subject to suppression from the fellow eye, generate weaker visual evoked potentials (VEPs) than fellow eyes and have multiple visual deficits including impairments in visual acuity and contrast sensitivity. Primate models and human psychophysics indicate that stronger suppression is associated with greater deficits in amblyopic eye contrast sensitivity and visual acuity. We tested whether transcranial direct current stimulation (tDCS) of the visual cortex would modulate VEP amplitude and contrast sensitivity in adults with amblyopia. tDCS can transiently alter cortical excitability and may influence suppressive neural interactions. Twenty-one patients with amblyopia and twenty-seven controls completed separate sessions of anodal (a-), cathodal (c-) and sham (s-) visual cortex tDCS. A...
Amblyopia is a neurodevelopmental disorder of vision that is associated with abnormal patterns of... more Amblyopia is a neurodevelopmental disorder of vision that is associated with abnormal patterns of neural inhibition within the visual cortex. This disorder is often considered to be untreatable in adulthood because of insufficient visual cortex plasticity. There is increasing evidence that interventions that target inhibitory interactions within the visual cortex, including certain types of noninvasive brain stimulation, can improve visual function in adults with amblyopia. We tested the hypothesis that anodal transcranial direct current stimulation (a-tDCS) would improve visual function in adults with amblyopia by enhancing the neural response to inputs from the amblyopic eye. Thirteen adults with amblyopia participated and contrast sensitivity in the amblyopic and fellow fixing eye was assessed before, during and after a-tDCS or cathodal tDCS (c-tDCS). Five participants also completed a functional magnetic resonance imaging (fMRI) study designed to investigate the effect of a-tDCS...
Approximately 3.2–5.3 million Americans live with the consequences of a traumatic brain injury (T... more Approximately 3.2–5.3 million Americans live with the consequences of a traumatic brain injury (TBI), making TBI one of the most common causes of disability in the world. Visual deficits often accompany TBI but physiological and anatomical evidence for injury in mild TBI is lacking. Axons traversing the corpus callosum are particularly vulnerable to TBI. Hemifield representations of early visual areas are linked by bundles of fibers that together cross the corpus callosum while maintaining their topographic relations. Given the increased vulnerability of the long visual axons traversing the corpus callosum, we hypothesized that inter-hemispheric transmission for vision will be impaired following mild TBI. Using the travelling wave paradigm (Wilson, Blake, & Lee 2001), we measured inter-hemispheric transmission in terms of both speed and propagation failures in 14 mild TBI patients and 14 age-matched controls. We found that relative to intra-hemispheric waves, inter-hemispheric waves were faster and that the inter-hemispheric propagation failures were more common in TBI patients. Furthermore, the transmission failures were topographically distributed, with a bias towards greater failures for transmission across the upper visual field. We discuss the results in terms of increased local inhibition and topographically-selective axonal injury in mild TBI.
Tinnitus is the conscious perception of sound with no physical sound source. Some models of tinni... more Tinnitus is the conscious perception of sound with no physical sound source. Some models of tinnitus pathophysiology suggest that networks associated with attention, memory, distress and multisensory experience are involved in tinnitus perception. The aim of this study was to evaluate whether a multisensory attention training paradigm which used audio, visual, and somatosensory stimulation would reduce tinnitus. Eighteen participants with predominantly unilateral chronic tinnitus were randomized between two groups receiving 20 daily sessions of either integration (attempting to reduce salience to tinnitus by binding with multisensory stimuli) or attention diversion (multisensory stimuli opposite side to tinnitus) training. The training resulted in small but statistically significant reductions in Tinnitus Functional Index and Tinnitus Severity Numeric Scale scores and improved attentional abilities. No statistically significant improvements in tinnitus were found between the training groups. This study demonstrated that a short period of multisensory attention training reduced unilateral tinnitus, but directing attention toward or away from the tinnitus side did not differentiate this effect.
Amblyopia is a visual disorder caused by poorly coordinated binocular input during development. L... more Amblyopia is a visual disorder caused by poorly coordinated binocular input during development. Little is known about the impact of amblyopia on the white matter within the visual system. We studied the properties of six major visual white-matter pathways in a group of adults with amblyopia (n = 10) and matched controls (n = 10) using diffusion weighted imaging (DWI) and fiber tractography. While we did not find significant differences in diffusion properties in cortico-cortical pathways, patients with amblyopia exhibited increased mean diffusivity in thalamo-cortical visual pathways. These findings suggest that amblyopia may systematically alter the white matter properties of early visual pathways.
Adults with amblyopia, a common visual cortex disorder caused primarily by binocular disruption d... more Adults with amblyopia, a common visual cortex disorder caused primarily by binocular disruption during an early critical period, do not respond to conventional therapy involving occlusion of one eye [1]. But it is now clear that the adult human visual cortex has a significant degree of plasticity [2], suggesting that something must be actively preventing the adult brain from learning to see through the amblyopic eye. One possibility is an inhibitory signal from the contralateral eye that suppresses cortical inputs from the amblyopic eye 3 and 4. Such a gating mechanism could explain the apparent lack of plasticity within the adult amblyopic visual cortex 5 and 6. Here we provide direct evidence that alleviating suppression of the amblyopic eye through dichoptic stimulus presentation induces greater levels of plasticity than forced use of the amblyopic eye alone. This indicates that suppression is a key gating mechanism that prevents the amblyopic brain from learning to see.
Amblyopia is a neurodevelopmental disorder of vision caused by abnormal visual experience during ... more Amblyopia is a neurodevelopmental disorder of vision caused by abnormal visual experience during early childhood that is often considered to be untreatable in adulthood. Recently, it has been shown that a novel dichoptic videogame-based treatment for amblyopia can improve visual function in adult patients, at least in part, by reducing inhibition of inputs from the amblyopic eye to the visual cortex. Non-invasive anodal transcranial direct current stimulation has been shown to reduce the activity of inhibitory cortical interneurons when applied to the primary motor or visual cortex. In this double-blind, sham-controlled cross-over study we tested the hypothesis that anodal transcranial direct current stimulation of the visual cortex would enhance the therapeutic effects of dichoptic videogame-based treatment. A homogeneous group of 16 young adults (mean age 22.1 ± 1.1 years) with amblyopia were studied to compare the effect of dichoptic treatment alone and dichoptic treatment combined with visual cortex direct current stimulation on measures of binocular (stereopsis) and monocular (visual acuity) visual function. The combined treatment led to greater improvements in stereoacuity than dichoptic treatment alone, indicating that direct current stimulation of the visual cortex boosts the efficacy of dichoptic videogame-based treatment. This intervention warrants further evaluation as a novel therapeutic approach for adults with amblyopia.
Background
Amblyopia is a neurodevelopmental disorder of vision that is associated with abnormal... more Background
Amblyopia is a neurodevelopmental disorder of vision that is associated with abnormal patterns of neural inhibition within the visual cortex. This disorder is often considered to be untreatable in adulthood due to insufficient visual cortex plasticity. There is increasing evidence that interventions which target inhibitory interactions within the visual cortex, including certain types of non-invasive brain stimulation, can improve visual function in adults with amblyopia.
Objective
We tested the hypothesis that anodal transcranial direct current stimulation (a-tDCS) would improve visual function in adults with amblyopia by enhancing the neural response to inputs from the amblyopic eye.
Methods
Thirteen adults with amblyopia participated and contrast sensitivity in the amblyopic and fellow fixing eye was assessed before, during and after a-tDCS or cathodal tDCS (c-tDCS). Five participants also completed an fMRI study designed to investigate the effect of a-tDCS on the BOLD response within the visual cortex to inputs from the amblyopic vs. the fellow fixing eye.
Results
A subgroup of 8/13 participants showed a transient improvement in amblyopic eye contrast sensitivity for at least 30 minutes after a-tDCS. fMRI measurements
3
indicated that the characteristic cortical response asymmetry in amblyopes which favours the fellow eye was reduced by a-tDCS.
Conclusions
These preliminary results suggest that a-tDCS deserves further investigation as a potential tool to enhance amblyopia treatment outcomes in adults.""""
Transcranial direct current stimulation (tDCS) is a safe, non-invasive technique for transiently ... more Transcranial direct current stimulation (tDCS) is a safe, non-invasive technique for transiently modulating the balance of excitation and inhibition within the human brain. It has been reported that anodal tDCS can reduce both GABA mediatedinhibition and GABA concentration within the human motor cortex. As GABA mediated inhibition is thought to be a keymodulator of plasticity within the adult brain, these findings have broad implications for the future use of tDCS. It isimportant, therefore, to establish whether tDCS can exert similar effects within non-motor brain areas. The aim of this studywas to assess whether anodal tDCS could reduce inhibitory interactions within the human visual cortex. Psychophysicalmeasures of surround suppression were used as an index of inhibition within V1. Overlay suppression, which is thought tooriginate within the lateral geniculate nucleus (LGN), was also measured as a control. Anodal stimulation of the occipitalpoles significantly reduced psychophysical surround suppression, but had no effect on overlay suppression. This effect wasspecific to anodal stimulation as cathodal stimulation had no effect on either measure. These psychophysical results providethe first evidence for tDCS-induced reductions of intracortical inhibition within the human visual cortex.
Amblyopia is a neurodevelopmental disorder of vision that occurs when the visual cortex receives ... more Amblyopia is a neurodevelopmental disorder of vision that occurs when the visual cortex receives decorrelated inputs from the two eyes during an early critical period of development. Amblyopic eyes are subject to suppression from the fellow eye, generate weaker visual evoked potentials (VEPs) than fellow eyes and have multiple visual deficits including impairments in visual acuity and contrast sensitivity. Primate models and human psychophysics indicate that stronger suppression is associated with greater deficits in amblyopic eye contrast sensitivity and visual acuity. We tested whether transcranial direct current stimulation (tDCS) of the visual cortex would modulate VEP amplitude and contrast sensitivity in adults with amblyopia. tDCS can transiently alter cortical excitability and may influence suppressive neural interactions. Twenty-one patients with amblyopia and twenty-seven controls completed separate sessions of anodal (a-), cathodal (c-) and sham (s-) visual cortex tDCS. A...
Amblyopia is a neurodevelopmental disorder of vision that is associated with abnormal patterns of... more Amblyopia is a neurodevelopmental disorder of vision that is associated with abnormal patterns of neural inhibition within the visual cortex. This disorder is often considered to be untreatable in adulthood because of insufficient visual cortex plasticity. There is increasing evidence that interventions that target inhibitory interactions within the visual cortex, including certain types of noninvasive brain stimulation, can improve visual function in adults with amblyopia. We tested the hypothesis that anodal transcranial direct current stimulation (a-tDCS) would improve visual function in adults with amblyopia by enhancing the neural response to inputs from the amblyopic eye. Thirteen adults with amblyopia participated and contrast sensitivity in the amblyopic and fellow fixing eye was assessed before, during and after a-tDCS or cathodal tDCS (c-tDCS). Five participants also completed a functional magnetic resonance imaging (fMRI) study designed to investigate the effect of a-tDCS...
Approximately 3.2–5.3 million Americans live with the consequences of a traumatic brain injury (T... more Approximately 3.2–5.3 million Americans live with the consequences of a traumatic brain injury (TBI), making TBI one of the most common causes of disability in the world. Visual deficits often accompany TBI but physiological and anatomical evidence for injury in mild TBI is lacking. Axons traversing the corpus callosum are particularly vulnerable to TBI. Hemifield representations of early visual areas are linked by bundles of fibers that together cross the corpus callosum while maintaining their topographic relations. Given the increased vulnerability of the long visual axons traversing the corpus callosum, we hypothesized that inter-hemispheric transmission for vision will be impaired following mild TBI. Using the travelling wave paradigm (Wilson, Blake, & Lee 2001), we measured inter-hemispheric transmission in terms of both speed and propagation failures in 14 mild TBI patients and 14 age-matched controls. We found that relative to intra-hemispheric waves, inter-hemispheric waves were faster and that the inter-hemispheric propagation failures were more common in TBI patients. Furthermore, the transmission failures were topographically distributed, with a bias towards greater failures for transmission across the upper visual field. We discuss the results in terms of increased local inhibition and topographically-selective axonal injury in mild TBI.
Tinnitus is the conscious perception of sound with no physical sound source. Some models of tinni... more Tinnitus is the conscious perception of sound with no physical sound source. Some models of tinnitus pathophysiology suggest that networks associated with attention, memory, distress and multisensory experience are involved in tinnitus perception. The aim of this study was to evaluate whether a multisensory attention training paradigm which used audio, visual, and somatosensory stimulation would reduce tinnitus. Eighteen participants with predominantly unilateral chronic tinnitus were randomized between two groups receiving 20 daily sessions of either integration (attempting to reduce salience to tinnitus by binding with multisensory stimuli) or attention diversion (multisensory stimuli opposite side to tinnitus) training. The training resulted in small but statistically significant reductions in Tinnitus Functional Index and Tinnitus Severity Numeric Scale scores and improved attentional abilities. No statistically significant improvements in tinnitus were found between the training groups. This study demonstrated that a short period of multisensory attention training reduced unilateral tinnitus, but directing attention toward or away from the tinnitus side did not differentiate this effect.
Amblyopia is a visual disorder caused by poorly coordinated binocular input during development. L... more Amblyopia is a visual disorder caused by poorly coordinated binocular input during development. Little is known about the impact of amblyopia on the white matter within the visual system. We studied the properties of six major visual white-matter pathways in a group of adults with amblyopia (n = 10) and matched controls (n = 10) using diffusion weighted imaging (DWI) and fiber tractography. While we did not find significant differences in diffusion properties in cortico-cortical pathways, patients with amblyopia exhibited increased mean diffusivity in thalamo-cortical visual pathways. These findings suggest that amblyopia may systematically alter the white matter properties of early visual pathways.
Adults with amblyopia, a common visual cortex disorder caused primarily by binocular disruption d... more Adults with amblyopia, a common visual cortex disorder caused primarily by binocular disruption during an early critical period, do not respond to conventional therapy involving occlusion of one eye [1]. But it is now clear that the adult human visual cortex has a significant degree of plasticity [2], suggesting that something must be actively preventing the adult brain from learning to see through the amblyopic eye. One possibility is an inhibitory signal from the contralateral eye that suppresses cortical inputs from the amblyopic eye 3 and 4. Such a gating mechanism could explain the apparent lack of plasticity within the adult amblyopic visual cortex 5 and 6. Here we provide direct evidence that alleviating suppression of the amblyopic eye through dichoptic stimulus presentation induces greater levels of plasticity than forced use of the amblyopic eye alone. This indicates that suppression is a key gating mechanism that prevents the amblyopic brain from learning to see.
Amblyopia is a neurodevelopmental disorder of vision caused by abnormal visual experience during ... more Amblyopia is a neurodevelopmental disorder of vision caused by abnormal visual experience during early childhood that is often considered to be untreatable in adulthood. Recently, it has been shown that a novel dichoptic videogame-based treatment for amblyopia can improve visual function in adult patients, at least in part, by reducing inhibition of inputs from the amblyopic eye to the visual cortex. Non-invasive anodal transcranial direct current stimulation has been shown to reduce the activity of inhibitory cortical interneurons when applied to the primary motor or visual cortex. In this double-blind, sham-controlled cross-over study we tested the hypothesis that anodal transcranial direct current stimulation of the visual cortex would enhance the therapeutic effects of dichoptic videogame-based treatment. A homogeneous group of 16 young adults (mean age 22.1 ± 1.1 years) with amblyopia were studied to compare the effect of dichoptic treatment alone and dichoptic treatment combined with visual cortex direct current stimulation on measures of binocular (stereopsis) and monocular (visual acuity) visual function. The combined treatment led to greater improvements in stereoacuity than dichoptic treatment alone, indicating that direct current stimulation of the visual cortex boosts the efficacy of dichoptic videogame-based treatment. This intervention warrants further evaluation as a novel therapeutic approach for adults with amblyopia.
Background
Amblyopia is a neurodevelopmental disorder of vision that is associated with abnormal... more Background
Amblyopia is a neurodevelopmental disorder of vision that is associated with abnormal patterns of neural inhibition within the visual cortex. This disorder is often considered to be untreatable in adulthood due to insufficient visual cortex plasticity. There is increasing evidence that interventions which target inhibitory interactions within the visual cortex, including certain types of non-invasive brain stimulation, can improve visual function in adults with amblyopia.
Objective
We tested the hypothesis that anodal transcranial direct current stimulation (a-tDCS) would improve visual function in adults with amblyopia by enhancing the neural response to inputs from the amblyopic eye.
Methods
Thirteen adults with amblyopia participated and contrast sensitivity in the amblyopic and fellow fixing eye was assessed before, during and after a-tDCS or cathodal tDCS (c-tDCS). Five participants also completed an fMRI study designed to investigate the effect of a-tDCS on the BOLD response within the visual cortex to inputs from the amblyopic vs. the fellow fixing eye.
Results
A subgroup of 8/13 participants showed a transient improvement in amblyopic eye contrast sensitivity for at least 30 minutes after a-tDCS. fMRI measurements
3
indicated that the characteristic cortical response asymmetry in amblyopes which favours the fellow eye was reduced by a-tDCS.
Conclusions
These preliminary results suggest that a-tDCS deserves further investigation as a potential tool to enhance amblyopia treatment outcomes in adults.""""
Transcranial direct current stimulation (tDCS) is a safe, non-invasive technique for transiently ... more Transcranial direct current stimulation (tDCS) is a safe, non-invasive technique for transiently modulating the balance of excitation and inhibition within the human brain. It has been reported that anodal tDCS can reduce both GABA mediatedinhibition and GABA concentration within the human motor cortex. As GABA mediated inhibition is thought to be a keymodulator of plasticity within the adult brain, these findings have broad implications for the future use of tDCS. It isimportant, therefore, to establish whether tDCS can exert similar effects within non-motor brain areas. The aim of this studywas to assess whether anodal tDCS could reduce inhibitory interactions within the human visual cortex. Psychophysicalmeasures of surround suppression were used as an index of inhibition within V1. Overlay suppression, which is thought tooriginate within the lateral geniculate nucleus (LGN), was also measured as a control. Anodal stimulation of the occipitalpoles significantly reduced psychophysical surround suppression, but had no effect on overlay suppression. This effect wasspecific to anodal stimulation as cathodal stimulation had no effect on either measure. These psychophysical results providethe first evidence for tDCS-induced reductions of intracortical inhibition within the human visual cortex.
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Papers by Daniel P. Spiegel
Amblyopia is a neurodevelopmental disorder of vision that is associated with abnormal patterns of neural inhibition within the visual cortex. This disorder is often considered to be untreatable in adulthood due to insufficient visual cortex plasticity. There is increasing evidence that interventions which target inhibitory interactions within the visual cortex, including certain types of non-invasive brain stimulation, can improve visual function in adults with amblyopia.
Objective
We tested the hypothesis that anodal transcranial direct current stimulation (a-tDCS) would improve visual function in adults with amblyopia by enhancing the neural response to inputs from the amblyopic eye.
Methods
Thirteen adults with amblyopia participated and contrast sensitivity in the amblyopic and fellow fixing eye was assessed before, during and after a-tDCS or cathodal tDCS (c-tDCS). Five participants also completed an fMRI study designed to investigate the effect of a-tDCS on the BOLD response within the visual cortex to inputs from the amblyopic vs. the fellow fixing eye.
Results
A subgroup of 8/13 participants showed a transient improvement in amblyopic eye contrast sensitivity for at least 30 minutes after a-tDCS. fMRI measurements
3
indicated that the characteristic cortical response asymmetry in amblyopes which favours the fellow eye was reduced by a-tDCS.
Conclusions
These preliminary results suggest that a-tDCS deserves further investigation as a potential tool to enhance amblyopia treatment outcomes in adults.""""
Amblyopia is a neurodevelopmental disorder of vision that is associated with abnormal patterns of neural inhibition within the visual cortex. This disorder is often considered to be untreatable in adulthood due to insufficient visual cortex plasticity. There is increasing evidence that interventions which target inhibitory interactions within the visual cortex, including certain types of non-invasive brain stimulation, can improve visual function in adults with amblyopia.
Objective
We tested the hypothesis that anodal transcranial direct current stimulation (a-tDCS) would improve visual function in adults with amblyopia by enhancing the neural response to inputs from the amblyopic eye.
Methods
Thirteen adults with amblyopia participated and contrast sensitivity in the amblyopic and fellow fixing eye was assessed before, during and after a-tDCS or cathodal tDCS (c-tDCS). Five participants also completed an fMRI study designed to investigate the effect of a-tDCS on the BOLD response within the visual cortex to inputs from the amblyopic vs. the fellow fixing eye.
Results
A subgroup of 8/13 participants showed a transient improvement in amblyopic eye contrast sensitivity for at least 30 minutes after a-tDCS. fMRI measurements
3
indicated that the characteristic cortical response asymmetry in amblyopes which favours the fellow eye was reduced by a-tDCS.
Conclusions
These preliminary results suggest that a-tDCS deserves further investigation as a potential tool to enhance amblyopia treatment outcomes in adults.""""