Dissociating entorhinal and hippocampal involvement in latent inhibition

This study used anatomical cues to suggest afunctional dissociation between the roles of the entorhinal cortex and the hippocampus in learning. The authors proposed that the highly convergent inputs to the entorhinal cortex indicate this region may be particularly important for selecting or compressing information. This hypothesis was tested in rabbits (Oryctolagus cunniculus) trained on an associative learning task that is a common index of stimulus selection. In this task, known as latent inhibition, preexposure toa stimulus (such as a tone) leads to slowed learning when the same tone is subsequently paired with an outcome (such as an airpuff to the eye). As hypothesized, rabbits with neurotoxic lesions of the entorhinal cortex failed to show slowed learning following preexposure (no latent inhibition) and learned the association faster than control rabbits. In contrast, hippocampal-lesioned animals showed normal (slowed) learning. The hippocampal region plays an important role in learning and memory. Studies in both humans and animals have demonstrated that damage to the hippocampal region results in a variety of learning and memory deficits, including anterograde amnesia (Squire, 1987), spatial-learning deficits (Morris, Garrud, Rawlins, & O'Keefe, 1982; O'Keefe & Nadel, 1978), and impairment on learning tasks requiring the use of configuration and contex