Neural Basis of Sensory Discrimination Learning

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DESCRIPTION (provided by applicant): The long-term objective of the application is a complete description and understanding of how the brain changes when a sensory discrimination is learned. The Principal Investigator has led recent technological advances that let cortical implants sample action potential responses from the same brain locations over many months. These advances provide the opportunity, for the first time, to study how the distributed generation of action potentials in the brain changes on a daily basis throughout the learning process. Our prior work has monitored animals throughout the learning process. In the first two days after selecting for targets and avoiding distractors, action potential responses to both task targets and non-targets increase several-fold, and receptive fields broaden spatially. With time, responsiveness returns to normal levels, and responses to task distractors become selectively suppressed. Our working hypothesis is that these plasticity effects depend only on cognitive reward associations. In the first study we will serially train implanted animals in detection and discrimination tasks in which the target assignment is kept constant, for several weeks at each task. This experiment will separate neuroplasticity effects that occur through associating rewards with task target stimuli and associating omission of reward with task distractors. Animals will then perform the same task with target and distractor assignments swapped, to reverse reward associations. Then, animals will be classically conditioned to the same stimuli, which preserve reward associations while introducing a broad range of behavioral changes; preliminary data shows minimal neuroplasticity results from this transition. Then, as a classical conditioning experiment, target and distractor reward associations will be reversed. Other studies will test coincident-input models of cortical plasticity against reward association models to determine which takes precedence when they are inconict. And lastly, studies will test hypotheses on how the neuroplasticity rules caused by these associations are implemented by the brain's neuromodulatory systems. Throughout each study, spike responses, local field potentials, and receptive fields in area 3b will be monitored before and during behavioral performance to create output measures to compare with behavioral data. This study proposes basic science investigations into circuitry underlying learning. It will lay the substrate for what is sure to be a very active area in public health in the coming decade. Abnormalities in these neuromodulatory centers, the Nucleus Basalis, Substantia Nigra, and Locus Coeruleus, are thought to be behind an array of neurological and mental disorders such as age-related cognitive decline, Alzheimer's disease, Parkinson's disease, Schizophrenia, General Depression, OCD, and addiction. Understanding how the brain changes when we learn will enable more targeted studies of how learning, and thus neuromodulatory activity, is abnormal in these neurological conditions. However, this is a basic science application, and so direct applicability to public health will depend upon follow-up applied studies.