Stimulating thoughts about heading perception

Abstract

When we move through the world it appears to expand, a phenomenon which is used to great effect in the Star Trek television series. We know where we are heading based on the pattern of expansion we see. This even holds when we make pursuit eye movements that add a motion component to the retinal image. But is there a correlate for heading perception in the brain? Some neurons in cortical area MSTd (the dorsal portion of the middle superior temporal region) of the macaque respond to expanding visual stimuli, and hence MSTd seems to be involved in the heading calculation. So far no evidence linking monkeys' heading perception and neural activity has been demonstrated. Now Britten and van Wezel show that activity in MSTd is correlated with the performance of monkeys in a heading task[ 1 Britten K.H. van Wezel R.J.A. Electrical microstimulation of cortical area MST biases heading perception in monkeys. Nature Neurosci. 1998; 1: 59-631 Crossref PubMed Scopus (228) Google Scholar ]. Neural activity in MSTd was recorded when monkeys saw expansion patterns. Based on this a prediction was made about the preferred heading of the particular electrode site. Next, the monkey had to indicate the perceived heading in a series of trials. On some trials a stimulation current was passed through the electrode. Thus, two psychometric functions were collected: for stimulated and unstimulated trials. For a large number of MSTd sites stimulation shifted the psychometric function, indicating that stimulation in MSTd affected the monkeys' response. About half of these sites showed the effect as predicted from the recordings. In additional experiments monkeys pursued the fixation point with their eyes during a trial. Strikingly, a majority of sites showed the expected effect of stimulation. While this difference between pursuit and non-pursuit trials is puzzling, these experiments are important because they provide the first evidence that MSTd activity is related to heading perception.