Temporal integration may be the brain's key step in generating flexible and intelligent behaviors that are divorced from the immediate time scales of sensory processing or motor execution. This research program aims to unpack the neural computations that underlie higher cognitive function by building off seminal studies in the primate dorsal stream and visual motion processing. Within an integrated framework of psychophysics, neurophysiology, and computation, we aim to ask precise questions about how fleeting sensory signals are read out to guide behavior, and to arrive at answers that span the levels of single neurons, neural circuits, and mental computations. This work strives to understand the basic mechanisms that deteriorate in a variety of mental health and brain aging conditions.
Aim 1. Precise characterization of temporal integration from stimulus to decision, using a reverse correlation protocol during psychophysics and simultaneous multiple-neuron / multiple-area recordings across MT and LIP, and interpreted via a generalized linear model. No empirical study has tested the hypothesized temporal integration of MT signals by LIP with direct measurement, which we will do by simultaneously recording from sets of MT and LIP neurons.
Aim 2. Causal interrogation of this (putative) decision-making circuit, extending the MT-LIP framework described above to include reversible inactivations of one area, complemented by concurrent multiple-neuron recordings in the other area. The evidence linking LIP to decision-making has been almost entirely correlation. We propose to perform inactivations of the area to test for its causal or necessary role in the accumulation of evidence.
Aim 3. Analysis of multiple stages of oculomotor decision-making, applying the multiple-neuron / multiple- area and inactivate-and-record approaches described in the aims above to LIP-FEF-PFC. Although the direct measurement of sensory signals in MT at the same time as LIP recording is likely to grant us significant new insights, the neural signals supporting motion discrimination almost certainly span a larger circuit with many sensory and cognitive stages. Here, we propose to apply the techniques described above to elucidate the relative roles of posterior parietal and prefrontal areas in decision-making.
Temporal integration is a fundamental building block of cognition, and the proposed research attempts to understand its neural implementation with a precision that allows for an appreciation of the relations between individual events and neural responses. Such precision is necessary for cognitive prosthetics to operate on the time scale of actual behaviors, as well as to understand basic mechanisms that deteriorate in many mental health and age-related diseases.
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