Topological Maps and Brain Computations From Low to High

Abstract

We first briefly summarize data from microelectrode studies on visual maps in non-human primates and other mammals, and characterize differences among the features of the approximately topological maps in the three main sensory modalities. We then explore the almost 50% of human neocortex that contains straightforward topological visual, auditory, and somatomotor maps by presenting a new parcellation as well as a movie atlas of cortical area maps on the FreeSurfer average surface, fsaverage. Third, we review data on moveable map phenomena as well as a recent study showing that cortical activity during sensorimotor actions may involve spatially locally coherent traveling wave and bump activity. Finally, by analogy with remapping phenomena and sensorimotor activity, we speculate briefly on the testable possibility that coherent localized spatial activity patterns might be able to ‘escape’ from topologically mapped cortex during ‘serial assembly of content’ operations such as scene and language comprehension, to form composite ‘molecular’ patterns that can move across some cortical areas and possibly return to topologically mapped cortex to generate motor output there.

The 3D Structural Architecture of the Human Hand Area is Non-Topographic

“…In human M1, large-scale body part representations are not only separated by low-myelin borders, but also differ in their microstructural profiles (Northall et al, 2022). This, together with our data, indicates that low-myelin borders and 3D structural differences coincide, providing evidence that large-scale body part representations can be regarded as distinct cortical fields (Sereno et al, 2022). In addition, our data suggests that small-scale body parts are structurally more integrated than large-scale body parts.…”

“…Recently, low-myelin borders have been identified in human S1 between major body part representations, which coincided with resting-state network separation (Glasser et al, 2016, Kuehn et al, 2017a). However, it is so far unknown whether such low-myelin borders also separate single finger representations in human S1, or whether the human hand area can be regarded as one, homogenous cortical field (Sereno et al, 2022).…”

“…In the somatosensory system, unlike in the visual system, topographic representations are discontinuous. That is, major body part representations, such as the hand and the face, are distinctly represented (Sereno et al, 2022). This representation of body parts in S1 reflects the discontinuous shape of the body in the real world, where the hand and the face, for example, are spatially distant (and can move independently) even though they cover neighboring areas in S1.…”

Layer-Specific Vulnerability is a Mechanism of Topographic Map Aging

“…We applied a systematic approach to characterize microstructure within the different cortical fields of M1 representing the LL, UL, and F areas in a sample of healthy adults. (1) We first hypothesized that M1, in healthy younger adults, is comprised of microstructurally-distinct cortical fields corresponding to topographic areas (as suggested by (Flechsig, 1920), also see (Glasser et al, 2016; Kuehn et al, 2017; Sereno et al, 2022)). (2) We further hypothesized that the microstructure of these cortical fields is also distinct in older adults, but that (3) the low-myelin borders between them (previously shown in younger adults, see Kuehn et al, 2017) are degenerated in older adults.…”

The role of awareness in shaping responses in human visual cortex

“…Specifically, we used regions V1, V2, and V3 from the probabilistic retinotopic atlas. In addition, we also used an atlas based on group-average maps [21] warped back into native brain space for each participant to automatically delineate larger clusters for V4, V3A/B, and the lateral occipital areas (LO). In each region of interest, we then calculated the correlation matrix of vertex-wise response patterns for all stimulus condition comparing the responses in odd-and even-numbered runs, respectively.…”