Penfield's Homunculus v. Integrate-Isolate Model
Published in Nature [1], 'A Somato-Cognitive Action Network Alternates with Effector Regions in Motor Cortex' found that "the classic homunculus is interrupted by regions with distinct connectivity, structure and function, alternative with effector-specific (foot, hand and mouth) areas" ([1], p351). The authors propose a dual-system of inter-effector and effector-isolating regions: the former coordinate whole-organism action and the later fine motor regions are "organised somatotopically as three concentric functional zones, with distal parts of the effector at the centre and proximal ones on the perimeter" ([1], p356).
To restate, the primary motor cortex (M1) is more complex than Penfield's classical homunculus [2, 3] can depict, leading to the novel "integrate-isolate" model ([1], Fig.4, p357) which represents organisational principles that are backed by large amounts of multi-modal data from fMRI precision functional mapping studies. The inter-effector regions have statistically significant projections from the cingulo-opercular network (the CON region localises goal-directed behaviours) to the effector-isolating regions of foot, hand and mouth ([1], Fig.2, p354), alongside minor degrees of functional specialisation between the three inter-effector regions.
"Human BCI recordings in M1, near the superior [inter-effector region], have also demonstrated whole-body movement tuning, possibly reflecting inter-effector activity and suggesting that the inter-effector motif could provide a target for whole-body BCI" ([1], p356). Of note, "...high-frequency signals may occur earlier in CON than in M1 - consistent with electrical recordings during voluntary movement - but that such signals reach the inter-effector [regions] earlier than the foot, hand and mouth regions" ([1], p353). This has potential implications for system latency optimisation in motor imagery BCIs.
The authors conclude that "the finding that action and body control are melded in a common circuit could help explain why mind and body states so often interact" ([1], p358). What do you think?
References
[1] https://doi.org/10.1038/s41586-023-05964-2
[2] https://doi.org/10.1093/brain/60.4.389
[3] Penfield, Wilder and Rasmussen, Theodore, "The Cerebral Cortex of Man" (1950). Jason W. Brown Library. 5.
https://digitalcommons.rockefeller.edu/jason-brown-library/5