Abstract
Functional magnetic resonance imaging (fMRI) at high magnetic fields has made it possible to investigate the columnar organization of the human brain in vivo with high degrees of accuracy and sensitivity. Until now, these results have been limited to the organization principles of early visual cortex (V1). While the middle temporal area (MT) has been the first identified extra-striate visual area shown to exhibit a columnar organization in monkeys, evidence of MT's columnar response properties and topographic layout in humans has remained elusive. Research using various approaches suggests similar response properties as in monkeys but failed to provide direct evidence for direction or axis of motion selectivity in human area MT. By combining state of the art pulse sequence design, high spatial resolution in all three dimensions (0.8 mm isotropic), optimized coil design, ultrahigh field magnets (7 Tesla) and novel high resolution cortical grid sampling analysis tools, we provide the first direct evidence for large-scale axis of motion selective feature organization in human area MT closely matching predictions from topographic columnar-level simulations.
Highlights
Vision is the human’s primary interface to the outside world
The regions identified as human MT area (hMT) lie within the posterior part of the superior temporal sulcus in close resemblance with the results of previous localization studies [17,18]
The existence of direction selective neurons within area middle temporal area (MT) is a well-established feature in the functional organization of higher visual cortex
Summary
Vision is the human’s primary interface to the outside world. To build a coherent percept, the visual system must computationally solve the problem of recognizing objects in a dynamic environment. In penetrations of single cell electrode recordings, neuronal response properties in many cortical areas remain relatively constant as one moves perpendicular to the surface of the cortex, while they vary in a direction parallel to the cortex Such columnar organization is evident in the visual system subdividing cortical territory in elementary units of operation, consisting of clusters of neurons sharing similar functional properties; in retinotopically organized visual areas cortical columns with the same feature selectivity are repeated several times each responding to different parts of the visual field. The overall MT complex was first discovered by Dubner & Zeki (1971) [3] while recording single cell responses in the anesthetized macaque; they observed a distinct organization of cells that were direction of motion selective While they proposed MT to be the first extrastriate area found to exhibit a columnar feature organization of direction selective neurons (DSN), corroborating evidence only came more than 10 years later [1,2]. Aggregated functional clusters responding to opposing motion directions are referred to as axis of motion columns
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