Locating primary somatosensory cortex in human brain stimulation studies: experimental evidence
Nicholas Paul Holmes1, Luigi Tamè2, Paisley Beeching1
1School of Psychology, University of Nottingham, University Park , Nottingham , United Kingdom.
Journal of Neurophysiology
|December 22, 2018
Summary
Researchers found the common method for locating the hand area of the primary somatosensory cortex (S1-hand) using transcranial magnetic stimulation (TMS) is inaccurate. New findings indicate S1-hand is lateral, not posterior, to the motor cortex, requiring reassessment of many TMS studies.
Area of Science:
- Neuroscience
- Neuroimaging
- Brain Stimulation
Background:
- Transcranial magnetic stimulation (TMS) requires precise targeting of brain regions.
- Current indirect methods for locating the primary somatosensory cortex hand area (S1-hand) are often inaccurate, as they rely on heuristics rather than individual neuroimaging data.
Purpose of the Study:
- To experimentally determine the accurate scalp location of the index finger area of the primary somatosensory cortex (S1-index).
- To provide an improved heuristic for S1-hand localization in TMS studies lacking individual MRI data.
Main Methods:
- Reanalyzed functional MRI data from 20 participants with vibrotactile stimulation.
- Constructed a probabilistic atlas of the central sulcus from 100 MRIs.
- Conducted TMS experiments assessing tactile discrimination performance.
- Examined neuronavigation data for S1-index scalp location.
Main Results:
- The S1-index scalp location is approximately 7-8 cm lateral to the vertex, near C3/C4 EEG electrode positions.
- S1-index is located approximately 2 cm lateral and 0.5 cm posterior to the primary motor cortex hand area (M1-hand) scalp location.
- This contradicts the common heuristic of locating S1-hand directly posterior to M1-hand.
Conclusions:
- The prevailing method for locating S1-hand using TMS requires immediate revision.
- The accuracy of numerous past TMS studies targeting S1-hand may be compromised and needs reassessment.
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