Nair, D. R. | Search bioRxiv

bioRxiv2026

Human frontal eye field and eyelid motor area revisited with electrical cortical stimulation and electrode co-registration

We investigated the anatomical localization of the frontal eye field (FEF) and its relationship to the eyelid motor area (EMA) and precentral motor cortex. We performed functional mapping using electrical cortical stimulation (ECS) and correlated electrode position by non-linear co-registration techniques using postoperative MRI. We studied 22 patients who underwent chronic implantation of subdural electrodes for epilepsy surgery. Eye movements were elicited at 52 electrodes overall. The majority of the movements were conjugated, saccadic eye deviation contralateral to the side of ECS. Head turning and non-saccadic eye deviation more frequently occurred in the vicinity of the precentral sulcus. Anatomically, FEF was located at Brodmanns area 6 in the most-caudal region of the middle frontal gyrus and in the adjacent part of the superior frontal sulcus and precentral sulcus. Functionally, FEF was situated at the level of the hand motor area, more dorsal than was described in Penfields motor homunculus. The FEF is situated anteriorly from the precentral motor cortex. The EMA was situated within the precentral motor cortex, partially overlapping with but distinctly ventral and caudal to FEF, and dorsal to the lower face motor area. A standardized map of the FEF and precentral motor homunculus is provided as a reference for human system neuroscience research.

neuroscience↗

bioRxiv2021

Local adaptation and archaic introgression shape global diversity at human structural variant loci

Large genomic insertions, deletions, and inversions are a potent source of functional and fitness-altering variation, but are challenging to resolve with short-read DNA sequencing alone. While recent long-read sequencing technologies have greatly expanded the catalog of structural variants (SVs), their costs have so far precluded their application at population scales. Given these limitations, the role of SVs in human adaptation remains poorly characterized. Here, we used a graph-based approach to genotype 107,866 long-read-discovered SVs in short-read sequencing data from diverse human populations. We then applied an admixture-aware method to scan these SVs for patterns of population-specific frequency differentiation--a signature of local adaptation. We identified 220 SVs exhibiting extreme frequency differentiation, including several SVs that were among the lead variants at their corresponding loci. The top two signatures traced to separate insertion and deletion polymorphisms at the immunoglobulin heavy chain locus, together tagging a 325 Kbp haplotype that swept to high frequency and was subsequently fragmented by recombination. Alleles defining this haplotype are nearly fixed (60-95%) in certain Southeast Asian populations, but are rare or absent from other global populations composing the 1000 Genomes Project. Further investigation revealed that the haplotype closely matches with sequences observed in two of three high-coverage Neanderthal genomes, providing strong evidence of a Neanderthal-introgressed origin. This extraordinary episode of positive selection, which we infer to have occurred between 1700 and 8400 years ago, corroborates the role of immune-related genes as prominent targets of adaptive archaic introgression. Our study demonstrates how combining recent advances in genome sequencing, genotyping algorithms, and population genetic methods can reveal signatures of key evolutionary events that remained hidden within poorly resolved regions of the genome.

evolutionary biology↗