Biology subjects

Wesselink, D. B.

Publications and source records attributed to Wesselink, D. B..

4 recordsLinked to original sources

bioRxiv2023

Does ipsilateral remapping following hand loss impact motor control of the intact hand?

What happens once a cortical territory becomes functionally redundant? We addressed brain and behavioural adaptations for the intact hand in individuals with a missing hand. Previous studies reported increased ipsilateral activity in the somatosensory territory of the missing hand (i.e., remapping) in acquired amputees, but not in individuals with a congenitally missing hand (one-handers). It is unclear whether remapping in amputees involves recruiting more neural resources to support the intact hand, and whether such activity is increased in tasks that demand greater motor control. We investigated sensorimotor learning and neural representation of the intact hand in one-handers and amputees using a multi-finger configuration task, as well as univariate and multivariate fMRI. We found that ipsilateral activity increased with motor demand - but only in the amputees group. However, these changes did not reflect behavioural differences. The representation of the finger configurations, as revealed by multivariate analysis, was stronger in amputees and closer to the typical representation found in controls contralateral hand territory, compared to one-handers. This collaborative contra-ipsilateral activity may reflect the intact hands efference copy. One-handers struggled to learn difficult finger configurations, but this did not translate to differences in univariate or multivariate activity relative to controls. Together with a supplementary structural white matter analysis, our results suggest that enhanced activity in the missing hand territory may not reflect intact hand function. Instead, we suggest that plasticity is more restricted than generally assumed and may depend on the availability of homologous pathways acquired early in life. Significant StatementWe studied whether brain resources in the missing-hand territory support demanding intact hand motor control in people who were born with one hand or lost a hand later in life. We found that amputees had increased activity in the brain area used for the missing hand, but no improvement in the performance of their intact hand. This collaborative contra-ipsilateral activity may reflect the intact hands efference copy. One-handers showed slight deficits while learning to perform complex motor movements, but no brain activity differences in the missing hand territory, compared to controls. Our results suggest that brain plasticity is limited and may depend on early life experiences.

neuroscience↗

bioRxiv2021

Finger representation in the cortex of the congenitally blind

Hand representation in the primary somatosensory cortex (S1) is thought to be shaped by experience. Individuals with congenital blindness rely on their sense of touch for completing daily tasks that in sighted people would be informed by vision, and possess superior tactile acuity. It has therefore been proposed that their S1 hand representation should differ from that of sighted individuals. Alternatively, it has been proposed that the improved tactile acuity in blind individuals is due to cross-modal plasticity, when regions in the occipital and temporal cortex are typically used for processing vision become activated by touch. We probed finger representation using psychophysics and 7T fMRI (1 mm3 resolution) in three individuals with bilateral anophthalmia, a rare condition in which both eyes fail to develop, as well as sighted controls. Despite anophthalmic individuals increased reliance on touch and superior tactile acuity, we found no evidence that they had more pronounced hand representation in S1. This is in line with recent research highlighting the stability of early sensory cortex, despite altered sensorimotor experience in adulthood. Unlike sighted controls, anophthalmic individuals activated the left human middle temporal complex (hMT+) during finger movement. This area did not express any hallmark of typical sensorimotor organisation, suggesting this and previously reported activity does not indicate low-level sensorimotor hand representation. However, left hMT+ contained some single finger information, beyond that found in sighted controls. This latter finding suggests that when the developmentally flexible area hMT+ is unaffected by retinal input, it can acquire novel cross-modal processes, which are potentially unrelated to the areas function in sighted people. As such, our findings highlight the opportunity for other organising principles, beyond domain specific plasticity, in shaping cross-modal reorganisation.

neuroscience↗

bioRxiv2020

Malleability of the cortical hand map following a finger nerve block

Individual fingers in the primary somatosensory cortex (S1) are known to be represented separately and adjacently, forming a cortical hand map. Electrophysiological studies in monkeys show that finger amputation triggers increased selectivity to the neighbouring fingers within the deprived S1, causing local reorganisation. Neuroimaging research in humans, however, shows persistent S1 finger representation of the missing hand, even decades after amputation. We aimed to resolve these apparently contrasting evidence by examining finger representation in humans following pharmacological amputation using single-finger nerve block and 7T neuroimaging. We hypothesised that beneath the apparent selectivity of individual fingers in the hand map, peripheral and central processing is distributed across fingers. If each finger contributes to the cortical representation of the others, then localised input loss will weaken finger representation across the hand map. For the same reason, the non-blocked fingers will stabilise the blocked fingers representation, resulting in persistent representation of the blocked finger. Using univariate selectivity profiling, we replicated the electrophysiological findings of local S1 reorganisation. However, more comprehensive analyses confirmed that local blocking reduced representation of all fingers across the entire hand area. Importantly, multivariate analysis demonstrated that despite input loss, representation of the blocked finger remained persistent and distinct from the unblocked fingers. Computational modelling suggested that the observed findings are driven by distributed processing underlying the topographic map, combined with homeostatic mechanisms. Our findings suggest that the long-standing depiction of the somatosensory hand map is misleading. As such, accounts for map reorganisation, e.g. following amputation, need to be reconsidered.

neuroscience↗

bioRxiv2019

Similar somatotopy for active and passive digit representation in primary somatosensory cortex

Scientists traditionally use passive stimulation to examine organisational properties of the primary somatosensory cortex (SI). Recent research has, however, emphasised the close and bidirectional relationship between somatosensory and motor systems. This suggests active contributions (e.g., direct inputs from the motor system to SI) should also be considered when studying SI representations. Under such a framework, discrepant results are possible when different tasks are used to study the same underlying somatosensory representation. Here we examined whether SI hand representation is consistent when compared between active and passive tasks. Moreover, we ask whether this holds when task demands and stimulus properties are not directly matched. Using 7T fMRI, we examined three key digit representation features - spatial location, activity gradient profiles and multivariate representational structure. We show that although activity was increased overall in the active task, all key features of digit somatotopy were consistent over tasks, using both traditional univariate (activity-level) and multivariate (pattern structure) measurements. Despite overall comparability, when investigating fine-grained features of somatotopy using multivariate analysis, the active task was superior for individuating the representation across digits. We suggest that the information produced by an active task is more aligned with typical, ecologically relevant patterns of hand sensory input, resulting in more optimal SI activity patterns. Our findings validate the utilisation of active tasks for studying SI somatotopy.

neuroscience↗