Four-dimensional maps of the human somatosensory system

Abstract

A fine-grained description of the spatiotemporal dynamics of human brain activity is a major goal of neuroscientific research. Limitations in spatial and temporal resolution of available noninvasive recording and imaging techniques have hindered so far the acquisition of precise, comprehensive four-dimensional maps of human neural activity. The present study combines anatomical and functional data from intracerebral recordings of nearly 100 patients, to generate highly resolved four-dimensional maps of human cortical processing of nonpainful somatosensory stimuli. These maps indicate that the human somatosensory system devoted to the hand encompasses a widespread network covering more than 10% of the cortical surface of both hemispheres. This network includes phasic components, centered on primary somatosensory cortex and neighboring motor, premotor, and inferior parietal regions, and tonic components, centered on opercular and insular areas, and involving human parietal rostroventral area and ventral medial-superior-temporal area. The technique described opens new avenues for investigating the neural basis of all levels of cortical processing in humans.A detailed description of the spatiotemporal dynamics of human brain activity is a major goal of neuroscientific research. However, it has been impossible so far to attain both high spatial and temporal resolution using the available noninvasive recording and imaging techniques. Hence, a precise and comprehensive four-dimensional cartography of human neural activity has not yet been obtained. High spatial resolution, provided by neuroimaging techniques such as functional magnetic resonance imaging (fMRI), is crucial for highlighting the topographical organization of specific areas (e.g., somatotopy of sensorimotor areas) as well as identifying the nodes of brain networks endowed with specific functional properties (1). It is not sufficient, however, to know which nodes are active; information is also needed about the local dynamics of the nodes, as well as the relative timing of their activity, to fully understand human brain functions (2, 3). Even if the temporal resolution of electroencephalography (EEG) and magnetoencephalography (MEG) allowed one to observe the intra-and interareal dynamics, to date such recordings remain too poor in localization power (1-2 cm) (3, 4). Combining EEG and fMRI has been suggested as a solution, using EEG to determine the temporal dynamics within and between the areas identified with fMRI (5). However, the disparate nature of the two signals recorded (hemodynamic for fMRI, electrical for EEG) creates discrepancies in the results that prevent precise matching of these methods (3).Invasive intracranial EEG offers a unique opportunity to observe human brain activity with an unparalleled combination of spatial and temporal resolution. Depending on the electrodes used, two kinds of recordings can be made: (i) intraparenchymal recordings, also called stereo-EEG (sEEG) (6), obtained using stereotactically inserted needle-like electrodes...

Stereo-EEG reveals rich cortical dynamics in humans coping with difficult action discrimination

“…Pathological activity was characterized by the presence of epileptic discharge at the seizure onset, but epileptic spikes could be present in leads exploring the regions surrounding the EZ during the interictal periods. Any trial presenting interictal epileptic discharges (IEDs) at any latency during the stimulus presentation was images (Avanzini et al 2016). Subsequently, multimodal views were constructed using the 3D Slicer software package (Fedorov et al 2012), and the exact position in the brain of all leads implanted in a single patient was determined by using multiplanar reconstructions (Dale et al 1999).…”

“…For each implanted patient, recordings started with the selection of an intracranial reference, computed as the average signal of two adjacent leads both exploring white matter. These leads were selected patient-by-patient by clinicians using the following criteria: no response to standard clinical stimulations, including somatosensory (median, tibial, and trigeminal nerves), visual (flash), and acoustical (click) stimulations, no sensory and/or motor behavior evoked by electrical stimulation (Avanzini et al 2016).…”

“…Alternatively, the negative results of Han and Marois (2013) and Wen et al (2018) may be due to technical limitations, imposed by the low temporal resolution of functional MRI (Ghuman and Martin 2019). Stereo EEG (sEEG) has millisecond temporal resolution, spatial resolution of a few mm (Parvizi and Kastner 2018), and by integrating data from multiple patients (Avanzini et al 2016) adequate coverage of the hemispheres. Therefore, the first aim of the present study was to investigate using sEEG, whether or not the MD system is involved in difficult action discrimination, by comparing cortical activity during action discrimination based on truncated and full videos.…”

Disentangling sound from syntax: electrophysiological analysis of linguistics expressions

“…Demographic data are shown in Table S3. In the remaining 10 subjects, a total of 164 electrodes were implanted (median 16.5 range [13][14][15][16][17][18][19], corresponding to 2186 recording contacts (median 210; range 168-272). The number of contacts in the grey matter was 1439 (65.8%); 586 recording contacts in the language dominant hemisphere (DH).…”

“…A detailed description of the localization of RCs for each patient can be found in Table S4. Figure 4 shows all RCs positioned and template-matched after warping each patient's MRI scan 15 .…”