Robert J. Sinclair

Cortical activity to vibrotactile stimulation: an fMRI study in blind and sighted individuals.

Blind individuals show visual cortex activity during Braille reading. We examined whether such cross‐modal activations reflect processing somatosensory stimuli independent of language by identifying cortical activity during a one‐back vibrotactile matching task. Three groups (sighted, early‐onset, and late‐onset [>12 years] blind) detected whether paired vibrations (25 and 100 Hz), delivered to the right index finger, differed in frequency. Three successive paired vibrations, followed by a no‐stimulation interval, were presented in a long event‐related design. A fixed effects average z‐score analysis showed increased activity throughout the visuotopic visual cortex, where it was mostly restricted to foveal and parafoveal eccentricities. Early blind showed the most extensive distribution of activity. Late blind exhibited activity mostly in similar regions but with declining response magnitudes with age of blindness onset. Three sighted individuals had suprathreshold activity in V1 but negative responses elsewhere in visual cortex. Mixed effects ANOVA confirmed group distinctions in defined regions (V1, V3, V4v, V7, LOC, and MT). These results suggest cross‐modal adaptation to tactile stimulation in visual cortex independent of language processes. All groups showed increased activity in left primary (S1) and bilateral second somatosensory areas, but without response magnitude differences between groups throughout sensorimotor cortex. Early blind showed the greatest spatial extent of S1 activity. Blind participants had more extensive bilateral activity in anterior intraparietal sulcus and supramarginal gyrus. Extensive usage of touch in Braille reading may underlie observed S1 expansions in the reading finger representation. In addition, learned attentiveness to touch may explain similar expansion of parietal tactile attention regions. Hum. Brain Mapp. 23:210–228, 2004.

Reading embossed capital letters: An fMRI study in blind and sighted individuals

Reading Braille activates visual cortex in blind people [Burton et al., J Neurophysiol 2002;87:589–611; Sadato et al., Nature 1996;380:526–528; Sadato et al., Brain 1998;121:1213–1229]. Because learning Braille requires extensive training, we had sighted and blind people read raised block capital letters to determine whether all groups engage visual cortex similarly when reading by touch. Letters were passively rubbed across the right index finger at 30 mm/s using an MR‐compatible drum stimulator. Age‐matched sighted, early blind (lost sight 0–5 years), and late blind (lost sight >5.5 years) volunteers performed three tasks: stating an identified letter, stating a verb containing an identified letter, and feeling a moving smooth surface. Responses were voiced immediately after the drum stopped moving across the fingertip. All groups showed increased activity in visual areas V1 and V2 during both letter identification tasks. Blind compared to sighted participants showed greater activation increases predominantly in the parafoveal‐peripheral portions of visuotopic areas and posterior parts of BA 20 and 37. Sighted participants showed suppressed activity in most of the same areas except for small positive responses bilaterally in V1, left V5/MT+, and bilaterally in BA 37/20. Blind individuals showed suppression of the language areas in the frontal cortex, while sighted individuals showed slight positive responses. Early blind showed a more extensive distribution of activity in superior temporal sulcal multisensory areas. These results show cross‐modal reorganization of visual cortex and altered response dynamics in nonvisual areas that plausibly reflect mechanisms for adaptive plasticity in blindness. Hum Brain Mapp, 2005.

Joint-Position Sense and Kinesthesia in Cerebral Palsy

OBJECTIVES To examine joint-position sense and kinesthesia in all extremities in participants with diplegic or hemiplegic cerebral palsy (CP). DESIGN Survey of joint-position sense and kinesthesia differences between aged-matched controls and 2 groups with CP. SETTING University movement assessment laboratory. PARTICIPANTS Population-based sample of participants with CP, diplegia (n=21), hemiplegia (n=17), and age-matched volunteers (n=21) without neurologic disease. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Joint-position sense and kinesthesia were measured in the transverse plane (forearm pronation/supination and hip internal/external rotation) using a custom-built device. For joint-position sense, participants actively rotated the tested limb to align the distal end with 10 target positions first with the limb and targets visible to assess their ability to perform the task motorically. The task was then repeated with vision of the limb occluded, with targets remaining visible. Joint-position sense error was determined by the magnitude and direction of the rotation errors for each limb in the vision and no vision conditions. Kinesthesia was evaluated by the ability to detect passive limb rotation without vision. RESULTS No group differences were detected in the vision condition. Indicative of joint-position sense deficits, a significant increase in errors was found in the no vision condition in all limbs except the dominant upper limb for both groups with CP. Joint-position sense errors were systematically biased toward the direction of internal rotation. Kinesthesia deficits were evident on the nondominant upper limb in diplegia and hemiplegia, and bilaterally in the lower limbs in hemiplegia. In hemiplegia, joint-position sense and kinesthesia deficits were noted on the dominant limbs, but were significantly worse on the nondominant limbs. CONCLUSIONS These results indicate that people with CP have proprioception deficits in all limbs.

Functional reorganization and stability of somatosensory-motor cortical topography in a tetraplegic subject with late recovery

The functional organization of somatosensory and motor cortex was investigated in an individual with a high cervical spinal cord injury, a 5-year absence of nearly all sensory/motor function at and below the shoulders, and rare recovery of some function in years 6–8 after intense and sustained rehabilitation therapies. We used functional magnetic resonance imaging to study brain activity to vibratory stimulation and voluntary movements of body parts above and below the lesion. No response to vibratory stimulation of the hand was observed in the primary somatosensory cortex (SI) hand area, which was conversely recruited during tongue movements that normally evoke responses only in the more lateral face area. This result suggests SI reorganization analogous to previously reported neuroplasticity changes after peripheral lesions in animals and humans. In striking contradistinction, vibratory stimulation of the foot evoked topographically appropriate responses in SI and second somatosensory cortex (SII). Motor cortex responses, tied to a visuomotor tracking task, displayed a near-typical topography, although they were more widespread in premotor regions. These findings suggest possible preservation of motor and some somatosensory cortical representations in the absence of overt movements or conscious sensations for several years after spinal cord injury and have implications for future rehabilitation and neural-repair therapies.

Cortical network for vibrotactile attention: A fMRI study

We used fMRI to identify brain areas activated during tactile attention tasks. Participants detected the interval containing target stimulation of higher vibrotactile frequency or longer duration. Attributes were selectively or neutrally cued. A control backwards‐counting task included concurrent, but irrelevant corresponding vibrotactile stimulation. Group analyses of average F‐statistic maps, participant conjunction maps, and estimated time courses utilized data mapped to a standard average surface atlas (PALS B12). Repeated‐measures, random‐effects MANOVA examined blood oxygenation level‐dependent (BOLD) signal modulation differences amongst tasks in defined regions, where significant responses occurred in at least 50% of the group. Greater than 0.1% increase in BOLD responses were found during at least one of the tactile attention tasks in contralateral parietal opercular OP1, BA 4 finger region, frontal eye field, dorsal premotor, anterior and posterior BA 7, and bilaterally in superior temporal sulcal cortex (BA 22), ventral premotor, supplementary motor area, and frontal operculum/insula. The same tasks suppressed activity in ipsilateral OP4. The BA 22 ROI showed larger responses during neutral cuing. The control task suppressed BOLD in ipsilateral OP1 and OP4 and bilaterally in BA 40, but significantly enhanced responses in dorsal parietal–frontal regions compared with tactile attention tasks. No regional differences were found between selectively cued frequency and duration tasks. Tactile attention effects were most prominent in OP1. Posterior parietal responses possibly reflected the visual attention required for backwards‐counting, whereas the frontal regions potentially related to goal‐directed behavior when identifying target stimulation. Hum Brain Mapp 2008.

Tactile sensory abilities in cerebral palsy: deficits in roughness and object discrimination

Motor deficits in cerebral palsy (CP) have been well documented; however, associated sensory impairment in CP remains poorly understood. We examined tactile object recognition in the hands using geometric shapes, common objects, and capital letters. Discrimination of tactile roughness was tested using paired horizontal gratings of varied groove widths passively translated across the index finger. We tested 17 individuals with hemiplegia (mean 13y 9mo [SD 5y 2mo]; 6 males, 11 females), 21 with diplegia (mean 14y 10mo [SD 7y]; 10 males, 11 females), and 21 without disabilities (mean 14y 10mo [SD 5y 1mo]; 11 males, 10 females). All participants with CP fell within level I or II of the Gross Motor Function Classification System and level I or II of the Manual Abilities Classification System. Individuals with CP were significantly less accurate compared with those without disabilities on all tactile object‐recognition tasks using their non‐dominant hand. Both groups of patients also had significantly higher thresholds for groove‐width differences with both hands compared with those without disabilities. Within the group with diplegia, only roughness discrimination differed between hands, whereas within the group with hemiplegia, significant between‐limb differences were present for all tasks. Despite mild motor deficits compared with the entire population of individuals with CP, this sample demonstrated ubiquitous tactile deficits.

Second somatosensory cortical area in macaque monkeys: 2. Neuronal responses to punctate vibrotactile stimulation of glabrous skin on the hand

Single neuron responses from the second somatosensory cortical area (SII) of macaque monkeys were studied using computer-controlled vibratory stimuli ranging in frequency from 10 to 300 Hz. Results were obtained using chronic recording techniques in awake or lightly tranquilized animals. Most neurons were unable to follow the temporal order of vibrations in excess of 10 Hz. A smaller sample of cells provided faithful reproduction of frequencies up to 50-75 Hz and another responded to low amplitude, high frequency stimulation in excess of 100 Hz. Cells that displayed temporally cohesive responses to lower frequencies demonstrated predictable, time-locked discharges to successive stimulus cycles. Cells activated by higher frequencies showed a lower probability of following successive stimulus cycles. These findings are discussed in reference to the hypothesis that SII may provide a parallel channel for processing high frequency vibrotactile inputs from Pacinian receptors.

Chapter 3 – Somatosensory Cortex and Tactile Perceptions

Publisher Summary This chapter considers the cerebral cortical areas responsible for low-threshold touch perception in primates. It emphasizes on cognitive factors in tactile perception, discusses receptive field organization in the cortex, and highlights the issues that may benefit from future study. On the basis of anatomical and physiological criteria, approximately ten parietal cortical areas involve somatosensory processing. These areas display separable cytoarchitecture and form a connected somatosensory network because they share thalamic and cortical connections. All ten areas respond in some way to cutaneous or deep receptor stimulation and most contain somatotopically-organized maps. The physiological perspective primarily focuses on the isolated elements responsible for perceptions of well-controlled tactile stimuli.

Tactile Discrimination of Gratings: Psychophysical and Neural Correlates in Human and Monkey

Human and monkey performance on discriminating tactile gratings revealed comparable cross-species Weber functions. Neural data obtained while monkeys performed discriminations revealed some matching of neural and psychometric functions. Nearly constant firing rate differences occurred at discrimination threshold for unequal groove widths. Firing rate differences of some cells decreased on trials preceding discrimination errors, and thus predicted performance.

Second somatosensory cortical area in macaque monkeys. I. Neuronal responses to controlled, punctate indentations of glabrous skin on the hand

Responses of 492 single neurons from the second somatosensory cortical area of macaque monkeys were studied using computer controlled ramp indentations. Results were obtained using chronic recording techniques from lightly tranquilized or awake animals. Amongst those cells that were activated by punctate tactile stimuli, various subclasses of responses were identified that included neurons with phasic and sustained adaptation characteristics. In addition, several cells showed unusual firing patterns, such as delayed responses and reverberating afterdischarges. Latency measurements from 90 cells showed a modal latency to ramp stimuli of 34 ms and a second group of cells whose latency exceeded 75 ms. Measurements of response functions to different velocities of indentation revealed that some cells maintained relatively shallow ascending functions but that most cells were insensitive to the velocity variable. The response characteristics of these neurons in primates are discussed in reference to the hypothesis that in the somatosensory cortex, SII occupies a higher order, serially dependent region in a hierarchy from SI to other parts of the brain.