Cortical Circuitry Underlying Memory-Guided Sensory Decisions

As we interact with our environment, the features of objects in the visual scene are not consistently present on the retina and sensory cues used to guide visual behavior are not always available. Thus, active observers are faced with a ubiquitous task of comparing stimuli across time and space. Our research program is aimed at examining the cortical circuitry underlying successful execution of sensory comparison tasks that involve visual motion. Such tasks require processing and storage of the initial stimulus, followed by its retrieval and comparison to the current stimulus, the process that leads to the perceptual decision. The mechanisms underlying such tasks are likely to involve brain regions that process and store sensory stimuli as well as regions that control visual attention and are capable of coordinating processes involving bottom-up sensory information and top-down cognitive signals.

To examine these mechanisms, we record neuronal activity with single and multi-laminar electrodes from the lateral prefrontal cortex (LPFC), implicated in attention, working memory and decision-making, and from area MT with well established role in the analysis of visual motion. By focusing on the sensory feature with well-understood neural coding, we are able to accurately track sensory representations in both cortical regions during sensory, maintenance, comparison and decision stages of the task, relate it to perceptual decisions. In addition to neuronal recording, we use local inactivation and microstimulation of LPFC to examine the role of its cognitive top-down signals in sensory processing and in perceptual decisions. The lab has an active ongoing collaboration with Dr. Albert Compte, the head of the Computational Neurobiology Lab at IDIBAPS (Barcelona, Spain), who has been developing biologically plausible computational models of working memory focusing on temporary storage of both spatial and motion information.

Our studies of the way LPFC represents and utilizes sensory signals during memory-guided visual comparison tasks have important implications for elucidating the basis of cognitive dysfunction in mental disorders long associated with deficits in sensory working memory and impaired prefrontal function.