Martuzzi, R. | Search bioRxiv

bioRxiv2022

Concurrent TMS-fMRI to determine adaptive brain changes to virtual lesions interfering with visual processing

Understanding how focal perturbations lead to large-scale network (re)organization is essential for accurately predicting the behavioral consequences of brain lesions. In this study, we applied a virtual lesion approach by means of short bursts of 10 Hz transcranial magnetic stimulation (TMS) over either early visual areas (EVA) or the medio-temporal area (MT) in healthy participants, while acquiring concurrent functional MRI. TMS delivered during the early stages of motion processing selectively impaired direction discrimination at both sites, while global motion perception remained unaffected. These behavioral effects were accompanied by a common local increase in BOLD activity, but distinct patterns of network reorganization. Perturbation of EVA led to more robust and efficient functional adaptation, suggesting greater resilience to focal disruption. In contrast, behavioral impairments following MT stimulation were associated with a less organized, more random network structure. Together, these findings underscore the potential of TMS-fMRI coupling as a powerful approach for mapping causal disconnectomics--the dynamic relationships between localized neural disruption and widespread functional and behavioral outcomes providing a better understanding of lesion-induced brain changes in neurological disorders such as stroke. HighlightsO_LITMS-induced perturbation of the early visual areas (EVA) or the mediotemporal area (MT) area selectively impairs motion direction discrimination. C_LIO_LIThe TMS perturbation is associated with a context-dependent local up-scaling of BOLD activity in both areas. C_LIO_LIThe two visual areas display distinct topological networks adaptation in response to TMS, reflecting different levels of network resilience to a focal lesion. C_LIO_LITMS-fMRI coupling can be used to assess causal disconnectomics and to precisely map how a local perturbation propagates to large-scale behavioural deficits. C_LI

neuroscience↗

bioRxiv2020

Palm-to-finger cortical functional interactions in primary somatosensory cortex: a 7T fMRI study

Many studies focused on the cortical representations of fingers, while the palm is relatively neglected despite its importance for hand function. Here, we investigated palm representation (PR) and its interactions with finger representations (FRs) in primary somatosensory cortex (S1). Few studies in humans suggested that PR is located medially with respect to FRs in S1, yet to date, no study directly quantified the somatotopic organization of PR and the five FRs. Importantly, the relationship between the somatotopic organization and the cortical functional interactions between PR and FRs remains largely unexplored. Using 7T fMRI, we mapped PR and the five FRs at the single subject level. First, we analyzed the cortical distance between PR and FRs to determine their somatotopic organization. Results show that the PR was located medially with respect to D5. Second, we tested whether the observed cortical distances would predict palm-finger functional interactions. Using three complementary measures of functional interactions (co-activations, pattern similarity and resting-state connectivity), we show that palm-finger functional interactions were not determined by their somatotopic organization, that is, there was no gradient moving from D5 to D1, except for resting-state connectivity, which was predicted by the somatotopy. Instead, we show that the representational geometry of palm-finger functional interactions reflected the physical structure of the hand. Collectively, our findings suggest that the spatial proximity between topographically organized neuronal populations do not necessarily predicts their functional interactions, rather the structure of the sensory space (e.g. the hand shape) better predicts the observed functional interactions.

neuroscience↗