In the published article, there was an error in Table 1 as published. The participant identifiers were not consistent with the text and figures. The corrected Table 1 and its caption appear below. The original table is not shown in this corrigendum because the participant identifiers were changed to improve participant confidentiality. The only change is the values in the "name" column.The authors apologize for this error and state that this does not change the scientific conclusions of the article in any way. The original article has been updated.
We used anatomical and functional magnetic resonance imaging (fMRI) at 4 Tesla to examine the damaged and spared brain regions in Patient MC, a 38-year old woman with Riddoch phenomenon - awareness of moving but not static stimuli. Anatomical scans indicated extensive damage to occipitotemporal cortex bilaterally and right posterior parietal cortex. Within occipital cortex, the only spared and visually active region was a small portion of the anterior calcarine cortex bilaterally. The expected location of the lateral occipital complex in neurologically intact subjects fell within the lesion, consistent with MC's absence of object-selective activation for both static and moving stimuli. Similarly, no face-, place- or body-selective activation for static or moving stimuli was observed. In contrast to the severe damage to early visual areas and ventral stream areas, numerous areas within the dorsal stream remained intact and functional. Consistent with MC's awareness of motion, fMRI revealed motion-selective activation bilaterally in the MT+ complex, just ahead of the occipitotemporal damage. Consistent with the preserved accuracy of her hand actions, MC showed robust grasp-selective activation in the anterior intraparietal area bilaterally and reach-selective activation in the superior parieto-occipital cortex of the left hemipshere. When shown movie clips of hands acting with tools, activation was observed in areas implicated in tool processing (intraparietal sulcus/supramarginal gyrus, middle temporal gyrus) and action observation (superior temporal sulcus). These results suggest that MC's dorsal stream continues to receive input either from a very limited extent of visual cortex or, more likely, from extrageniculostriate projections, two possibilities currently under investigation with diffusion tensor imaging. In sum, the damaged and activated regions within MC's brain are highly consistent with her behavioral deficits (Goodale et al., VSS 2008) in ventral stream functions (recognition) and her preserved abilities for several dorsal stream functions (motion perception, reaching, grasping, and tool observation).
Abstract When exposed to novel dynamical conditions (e.g., externally imposed forces), neurologically intact subjects easily adjust motor commands on the basis of their own reaching errors. Subjects can also benefit from visual observation of others' kinematic errors. Here, using fMRI, we scanned subjects watching movies depicting another person learning to reach in a novel dynamic environment created by a robotic device. Passive observation of reaching movements (whether or not they were perturbed by the robot) was associated with increased activation in fronto-parietal regions that are normally recruited in active reaching. We found significant clusters in parieto-occipital cortex, intraparietal sulcus, as well as in dorsal premotor cortex. Moreover, it appeared that part of the network that has been shown to be engaged in processing self-generated reach error is also involved in observing reach errors committed by others. Specifically, activity in left intraparietal sulcus and left dorsal premotor cortex, as well as in right cerebellar cortex, was modulated by the amplitude of observed kinematic errors.
Abstract The current study used a high frequency TMS protocol known as continuous theta burst stimulation (cTBS) to test a model of hand choice that relies on competing interactions between the hemispheres of the posterior parietal cortex. Based on the assumption that cTBS reduces cortical excitability, the model predicts a significant decrease in the likelihood of selecting the hand contralateral to stimulation. An established behavioural paradigm was used to estimate hand choice in each individual, and these measures were compared across three stimulation conditions: cTBS to the left posterior parietal cortex, cTBS to the right posterior parietal cortex, or sham cTBS. Our results provide no supporting evidence for the interhemispheric competition model. We find no effects of cTBS on hand choice, independent of whether the left or right posterior parietal cortex was stimulated. Our results are nonetheless of value as a point of comparison against prior brain stimulation findings that, in contrast, provide evidence for a causal role for the posterior parietal cortex in hand choice. Highlights High-frequency TMS applied to the left and right posterior parietal cortex, separately, did not produce reliable aftereffects on hand choice. Response times to initiate actions were significantly increased when reaching near the point in space where hand choice was equally probable.
We used an event-related fMRI adaptation paradigm to investigate changes in BOLD activity in the dorsal and ventral visual streams as a function of object identity and object orientation. On the basis of earlier work (James et al), we expected that areas in the dorsal stream would show sensitivity to changes in object orientation independent of object form whereas areas in the ventral stream would show sensitivity to changes in object form independent of object orientation. Participants (N=7) were presented with successive paired images of real-world, graspable objects, separated by a brief visual mask. The second image of each pair was either: i) identical in form and orientation to the first image, ii) identical in form but different in orientation iii) different in form but identical in orientation, or iv) different in both form and orientation. We identified distinct regions in the posterior cerebral cortex that were differentially sensitive to changes in form and orientation. In the dorsal stream, an area within the cIPS, extending into the superior occipital gyrus, showed a selective increase in BOLD activity with changes in object orientation. This same region was insensitive to changes in object form. In the ventral stream, areas within the LOC showed a selective increase in activity with changes in object form but were insensitive to changes in orientation. The differential sensitivity to object orientation and object form in these regions is consistent with the division of labour between the two streams. The dorsal stream, which plays a critical role in the visual control of actions such as grasping, might be expected to have networks that are particularly sensitive to the orientation of a goal object independent of its identity. By the same token, the ventral stream, which mediates object recognition, should have networks that are sensitive to the identity of objects independent of their orientation.
How and where in the human brain high-level sensorimotor processes such as intentions and decisions are coded remain important yet essentially unanswered questions. This is in part because, to date, decoding intended actions from brain signals has been primarily constrained to invasive neural recordings in nonhuman primates. Here we demonstrate using functional MRI (fMRI) pattern recognition techniques that we can also decode movement intentions from human brain signals, specifically object-directed grasp and reach movements, moments before their initiation. Subjects performed an event-related delayed movement task toward a single centrally located object (consisting of a small cube attached atop a larger cube). For each trial, after visual presentation of the object, one of three hand movements was instructed: grasp the top cube, grasp the bottom cube, or reach to touch the side of the object (without preshaping the hand). We found that, despite an absence of fMRI signal amplitude differences between the planned movements, the spatial activity patterns in multiple parietal and premotor brain areas accurately predicted upcoming grasp and reach movements. Furthermore, the patterns of activity in a subset of these areas additionally predicted which of the two cubes were to be grasped. These findings offer new insights into the detailed movement information contained in human preparatory brain activity and advance our present understanding of sensorimotor planning processes through a unique description of parieto-frontal regions according to the specific types of hand movements they can predict.
The current study used a high frequency TMS protocol known as continuous theta burst stimulation (cTBS) to test a model of hand choice that relies on competing interactions between the hemispheres of the posterior parietal cortex. Based on the assumption that cTBS reduces cortical excitability, the model predicts a significant decrease in the likelihood of selecting the hand contralateral to stimulation. An established behavioural paradigm was used to estimate hand choice in each individual, and these measures were compared across three stimulation conditions: cTBS to the left posterior parietal cortex, cTBS to the right posterior parietal cortex, or sham cTBS. Our results provide no supporting evidence for the interhemispheric competition model. We find no effects of cTBS on hand choice, independent of whether the left or right posterior parietal cortex was stimulated. Our results are nonetheless of value as a point of comparison against prior brain stimulation findings that, in contrast, provide evidence for a causal role for the posterior parietal cortex in hand choice.
Animal models reveal that deafferenting forelimb injuries precipitate reorganization in both contralateral and ipsilateral somatosensory cortices. The functional significance and duration of these effects are unknown, and it is unclear whether they also occur in injured humans. We delivered cutaneous stimulation during functional magnetic resonance imaging (fMRI) to map the sensory cortical representation of the intact hand and lower face in a group of chronic, unilateral, upper extremity amputees (N = 19) and healthy matched controls (N = 29). Amputees exhibited greater activity than controls within the deafferented former sensory hand territory (S1f) during stimulation of the intact hand, but not of the lower face. Despite this cortical reorganization, amputees did not differ from controls in tactile acuity on their intact hands. S1f responses during hand stimulation were unrelated to tactile acuity, pain, prosthesis usage, or time since amputation. These effects appeared specific to the deafferented somatosensory modality, as fMRI visual mapping paradigm failed to detect any differences between groups. We conclude that S1f becomes responsive to cutaneous stimulation of the intact hand of amputees, and that this modality-specific reorganizational change persists for many years, if not indefinitely. The functional relevance of these changes, if any, remains unknown.
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