The bilateral GM Primary motor cortex BA4a R, as defined in the Juelich maxprob thr25 2mm atlas, corresponds to a subregion of Brodmann area 4 located in the precentral gyrus of the frontal lobe, forming part of the primary motor cortex responsible for the execution of voluntary movements. This region contains large pyramidal neurons (Betz cells) that give rise to corticospinal projections, particularly influencing contralateral skeletal muscle activity via the pyramidal tract. Functionally, BA4a participates in fine motor control, force generation, and the precise timing of movement, integrating inputs from premotor and somatosensory areas while contributing to motor output to spinal motor circuits. There is no direct Wikipedia article specifically for “BA4a”; a closely related and encompassing structure is the Primary motor cortex.
The bilateral GM primary motor cortex BA4a (Juelich maxprob thr25 2mm) has been implicated in several genetic and GWAS findings related to motor control, neurodevelopmental and neurodegenerative disorders, and complex behavioral traits. Imaging-genetics studies using SNP-based and polygenic approaches have associated variation in this region’s cortical thickness, surface area, and activation with loci near genes involved in synaptic function and neuronal development (e.g., BDNF, CNTNAP2, CACNA1C, GRIN2B), as well as with general brain morphology loci identified in large-scale consortia (ENIGMA, UK Biobank) that highlight genes such as HMGA2 and IGF1. Motor cortex BA4a has repeatedly shown altered structure and function in monogenic and polygenic forms of motor neuron disease (including ALS genes like C9orf72, SOD1, TARDBP, FUS), hereditary spastic paraplegia, and dystonia, and is a key cortical target of risk loci for multiple sclerosis and cerebral palsy through effects on motor pathways. GWAS of handedness, fine motor skills, and physical activity have reported enrichment of associated variants in regulatory elements active in primary motor cortex, and polygenic risk for schizophrenia, ADHD, and autism spectrum disorder has been linked to microstructural and activation changes in BA4a, supporting a broader role of genetic variation in this region in both motor and higher-order behavioral phenotypes.
Overview generated by GPT-4o (2026).
Region ID: 48
Hemisphere: bilateral
Atlas: Juelich maxprob thr25 2mm
Full Quality Version: Download MP4
Full Quality Version: Download MP4
Wali Sidiqyar*, Gaurav Rudravaram*, Elyssa M. McMaster, Trent M. Schwartz, Adam M. Saunders, Kurt G. Schilling, Bennett A. Landman "Introducing SPINS: A Shared Public Visualization Library of Neuroanatomical Structures." Medical Imaging with Deep Learning- short paper
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