Decision related activity and top-down modulations in primate V1

What are the sources of trial-to-trial variability in neural responses in early sensory cortical areas and how does this variability affect perceptual decisions? In this talk I will describe results from two studies that aim to address these questions. In the first study, we examined co-variations between behavioral choices of monkeys performing a threshold visual detection task and neural population responses recorded simultaneously from their V1.  We found that fluctuations in V1 responses to the same visual stimulus are correlated with fluctuations in perceptual decisions. Our results provide insight regarding the decoding mechanisms that mediate behavior based on V1 responses and suggest that most choice-related variability is already present in V1.  Top-down modulations from higher visual cortical areas are one potential source for these decision related signals in V1. The goal of the second study was to characterize two forms of top-down effects in V1: modulations by spatial uncertainty and by stimulus relevance. We found that V1 responses are unaffected by spatial uncertainty, suggesting that target sensitivity is not a limited resource that can be improved by focal attention in V1. Conversely, V1 responses were significantly modulated by stimulus relevance. These modulations are likely to contribute to spatial gating of task-irrelevant information. However, the spatial and temporal characteristics of this top-down signal suggest that it is not a major source of choice-related variability in V1. Our results are therefore consistent with a predominantly bottom-up source of decision related activity in V1.