A recent study published in Cerebral Cortex proved that the motion direction signals in macaque middle temporal area are causally involved in heading perception based on visual optic flow cue. This work was performed by researchers from Dr. GU’s lab at the Institute of Neuroscience of Chinese Academy of Sciences.

Combining multiple techniques including psychophysics, in vivo extracellular recording and electrical microstimulation, the authors provide direct neurophysiological evidence showing that Middle Temporal Area (MT) neurons typically contain small receptive fields compared to the wide field, and they are highly responsive under optic flow experienced during natural navigation. Furthermore, the responses from MT neurons are weighted pooled by downstream brain areas for global heading computation

When animals navigate in the world, the surrounding objects generate a radial pattern of flow on the retina, the so-called optic flow. Optic flow is informative about the current motion status such that human and nonhuman primates can reliably discriminate heading direction as small as a few degrees based on it. Although this process might be mediated by the MT-MSTd circuits in the dorsal visual pathway, as proposed in many computational works, direct neurophysiological evidence is lacking.

Researchers first introduced an extra leftward or rightward motion vector into a small part of the optic flow that occupied the whole visual display. Human and monkey subjects were instructed to infer their self moving directions, i.e. heading based on global optic flow. They found that the subjects’ choices were biased by the introduced local perturbation cues. Meanwhile, neuronal recordings in the middle temporal (MT) area showed a similar bias shift in their tuning functions.

To examine a potential causal relationship between the MT responses and behavioral performance, they artificially perturbed monkeys’ MT activity by applying electrical microstimulation. They found that the microstimulation could significantly bias the monkeys’ choice predicted from the tuning of the stimulated neurons. In contrast to previous experiments in literature, this microstimulation effect remained even when masking the visual stimulus within the neurons’ receptive fields, supporting a pooling effect from local motion information embedded in MT for global heading perception formation.

This work was supported by grants from the National Natural Science Foundation of China Project (31471048), the Strategic Priority Research Program of CAS (XDB02010000), National Key Basic Research Project of China (2016YFC1306801), and the Shanghai Key Basic Research Project (16JC1420201).