Associative recall of sensory experiences is part-and-parcel of perception. Through a ubiquitous and automatic process, incomplete, noisy and ambiguous signals ascending from the sensory periphery are fleshed-out and disambiguated by associative memories. Consistent with this view, functional brain imaging studies in humans have shown that recall of visual pictorial memories is correlated with top-down activation of the same cortical areas that process incoming visual stimuli. Using a combination of neurophysiological and behavioral approaches, we have recently begun to explore top-down associative recall signals at the cellular level in primate visual cortex, and to relate these cellular signals to visual imagery and perception. Most importantly, we have discovered highly specific associative recall signals in cortical visual area MT, an area that plays a central role in visual motion processing. Our findings suggest a novel model system for detailed quantitative investigation of the functions and neuronal mechanisms of pictorial memory recall. We have proposed a series of neurophysiological and behavioral experiments designed to improve understanding of the source and plasticity of top-down recall signals, their distribution throughout visual cortex, and the interactions between recall and bottom-up visual sensations. By these means we hope to reveal the dynamic interplay between memory, imagery and perception. The long-term goal of this project is to contribute to the understanding of biological substrates of perception and cognition. Detailed knowledge of the normal functions of visual cortex shall provide insights into the neural events that underlie visual memory, imagery, dreaming and manifestations of perceptual disorders, such as hallucinations. Such information will ultimately aid in the treatment and prevention of neurological and neuropsychiatric disorders of visual perception and memory.
These aims are pertinent to the development and use of prosthetic, behavioral, and pharmacological therapies for the visually and mnemonically handicapped. ? ? ?
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