Cerebellum and Eyeblink Conditioning 50 Derick H. Lindquist, Joseph E. Steinmetz, and Richard F. Thompson Abstract The cerebellum and brainstem constitute the essential neural circuit responsible for the acquisition and expression of the classically conditioned eyeblink response in numerous mammalian species, including humans. In this simple form of motor learning, a neutral conditioned stimulus (CS) overlaps and coterminates with a mildly aversive unconditioned stimulus (US), resulting, eventually, in the production of an eyeblink conditioned response (CR) to the CS alone. The forebrain is engaged when this basic delay procedure is made more difficult – for instance, if the CS and US are separated by a brief stimulus- free gap of time. In either case, it is generally accepted that the critical memory trace is formed and stored in the cerebellar interpositus nucleus (IP). The cerebellar cortex also plays a key role in normal acquisition by modulating the amplitude and/or timing characteristics of the eyeblink CR. Owing to the well- defined nature of the neural circuit, and the close correspondence between animal and human studies, eyeblink conditioning has been successfully used to investigate cerebellar dysfunction across a variety of human populations. Herein, research related to three representative disorders is discussed: fetal D.H. Lindquist (*) Department of Psychology, The Ohio State University, 1835 Neil Ave., Room 49, 43210 Columbus, OH, USA e-mail: lindquist.40@osu.edu J.E. Steinmetz Department of Psychology, The Ohio State University, 230 N. Oval Mall, 43210 Columbus, OH, USA e-mail: steinmetz.53@osu.edu R.F. Thompson Department of Psychology, University of Southern California, 3641 Watt Way HNB-522, 90089 Los Angeles, CA, USA e-mail: thompson@usc.edu M. Manto, D.L. Gruol, J.D. Schmahmann, N. Koibuchi, F. Rossi (eds.), Handbook of the Cerebellum and Cerebellar Disorders, DOI 10.1007/978-94-007-1333-8_50, # Springer Science+Business Media Dordrecht 2013 1175