Neural Networks of Learning and Memory; Nutrition and Hippocampal Development; Neurophysiology of Aging and Learning

The primary focus of my laboratory is to understand how neuronal networks process and store information during learning. Along these lines, we would also like to know how nutrition affects the early development of these networks. Much of this research concentrates on an area of the brain called the hippocampus. This is one of the most important brain areas for acquiring and processing new information for later long-term storage. To understand how neuronal networks within the hippocampus and other structures encode learned information, we use single neuron electrophysiological recording techniques. These techniques measure the firing of electrical impulses (i.e., action potentials) transmitted by the single neurons within these networks. This electrophysiological recording technique has been optimized so that electrical signals can be recorded simultaneously from approximately 10 to 100 single neurons from the hippocampus of a single rat. These electrical signals are recorded while the rat performs a learning task called trace fear conditioning. This learning task requires the association of an auditory conditioned stimulus (CS) and an aversive unconditioned stimulus (US). What is most important about this task is that each time the CS and US are presented they are separated by a silent 20-second trace interval. We have used these techniques to show that neurons in different subdivisions of the hippocampus exhibit different firing patterns during trace fear conditioning (Gilmartin & McEchron, 2005a). Another project has shown that single neurons in the medial prefrontal cortex may interact with the hippocampus to encode information during trace classical conditioning (Gilmartin & McEchron, 2005b).


Other projects in our laboratory are determining how developmental nutritional deficits impair the physiology of learning and memory areas of the brain. These projects show that the development of the hippocampus and learning ability can be severely compromised by early nutritional deficits in iron. Moreover, we have shown that rats that receive an iron deficient diet during early development later show altered synaptic efficacy in the hippocampus. These young iron deficient rats also show impairments in hippocampus-dependent learning ability. Specifically, the data below show that rats that receive an iron deficient diet during the perinatal period show impaired trace fear conditioning (McEchron et al., 2005). We also used an in-vitro brain slice preparation to show that pathways in the hippcoampus show reduced synaptic efficacy as the result of the perinatal iron deficient diet (McEchron & Paronish, 2005).