The influence of hippocampus on habituation of the HSR task. Roberta Wiediger, Fran McSweeney & Jay Wright Psychology Department - Washington State University Introduction The hippocampus is one of the most important structures in the mammalian brain linked to learning and memory storage. It has the ability to pass information from one neuron to another, to reconfigure and consolidate information thus exhibiting synaptic plasticity. Habituation has been defined as a decrease in responsiveness to repeated presentation of a stimulus (Groves & Thompson, 1970). It is the simplest for of learning (Harris, 1943). The waning of a reflexive response to repeated stimulation (Staddon, 2001). Characteristic of habituation McSweeney and Murphy (2000) 14 characteristics E.g. Spontaneous recovery – the recovery of a habituated stimulus when that stimulus is not presented for a period of time. The Present Study The purpose of this experiment was to determine the role of the hippocampus during habituation of the HSR task during a classical conditioning paradigm (introduction of a tone), by using hippocampectomized rats. Method Subjects – 32 male Sprague- Dawley rats Apparatus – wood pedestal Tone – 74dB Air stimulus applied to the ear Surgeries Hippocampectomy Neocortex control Behavioral Testing HSR task 5-min adaptation period 24 trial – 15s stimulus presentation (air) ITI of 15s IBM compatible computer signaled the intervals Green – 15s of air presentation Red – 15s of ITI Association Tone session Same procedure as standard habituation session But A tone was introduced 1s preceding air presentation Groups 4 groups of rats (8 per group) All were tested over 2 habituation sessions with a 24h ITI. Group 1 – standard habituation Group 2 – tone habituation Group 3 – hippocampectomized tone Group 4 – neocortex control tone Predictions 1. Spontaneous recovery of the HSR was predicted for the standard habituation group after 24hISI but NOT for the tone habituation group. 2. Spontaneous recovery of the HSR was expected to occur in the hippocampectomized group but NOT for the neocortex group. 3. It was anticipated that the pattern of responding for the tone habituation group would be similar to the neocortex tone group. Results Discussion These data suggest that the tone is an important component for the HSR task to become associative This implies that the hippocampus is indeed important for associative learning to take place. However, the hippocampus is not important for the habituation of a non-associative task References Groves, P. M., & Thompson, R. F. (1970). Habituation: A dual-process theory. Psychological Review, 77, Harris, J.D., (1943). Habituation response decrement in the intact organism. Psychological Bulletin, 40, Murphy, E. S., McSweeney, F. K., & Kowal, B. P. (2003). Within-session decrease in operant responding as a function of pre-session feedings. The Psychological Record, 53, Staddon, J. E. R., (2001). The new behaviorism. Philadelphia, PA: Taylor & Francis. HSR session 1 = Mean 6.3 HSR session 2 = Mean 5.2 HSR Tone session 1 = Mean 6.6 HSR session 2 = Mean 2.8 HSR No hip session 1 = Mean 9.1 HSR session 2 = Mean 7.8 HSR Neocor session 1 = Mean 8.3 HSR session 2 = Mean 4.5 HSR