The cerebellum plays a crucial role in classical eyelid-blink conditioning (in this procedure, a puff of air, or shock near the eye, is the US, a tone is the CS, and blinking is the UR/CR; for reviews see Thompson and Krupa, 1994; Bloedel and Bracha, 1995). The following presents the findings of the research into this phenomenon using human subjects, which has been reviewed by Daum and Schugens (1996).

Two separate experiments, both using simple delay CS-US procedures, found that learning of the eyeblink response in human subjects with cerebellar damage was seriously impaired (Daum et al, 1993; Topka et al, 1993). Furthermore, these subjects had normal blink responses to the US, so physical difficulties could not be the cause of these results. It should be noted that some subjects with cerebellar damage did acquire the CR, although most of these subjects had mild brain damage. Studies of the effects of damage on brain structures traditionally associated with memory, such as the thalamus and medial temporal lobes, has shown that lesions to these structures typically does not affect eyeblink conditioning.

The role of the cerebellum in human eyeblink conditioning is also supported by studies on aging. As the cerebellum goes through changes when the body ages (such as a loss of Purkinje cells), CR frequency has been found to decrease. Similar supporting evidence comes from studies of autism. People with autism, which has been shown to have a relation to cerebral abnormalities, have also shown irregular patterns of CR acquisition.

Damage to the cerebellum does not interfere with other kinds of classical conditioning, such as the conditioning of electrodermal responses. Therefore, although the cerebellum plays a primary role in eyeblink conditioning in humans and animals, it does not appear that it is crucial to all kinds of classical conditioning.

References
Bloedel, J.R., & Bracha, V. (1995). On the cerebellum, cutaneomuscular reflexes, movement control and the elusive engrams of memory. Behavioural Brain Research, 68, 1-44.

Daum, I., & Schugens, M.M. (1996). On the cerebellum and classical conditioning. Current Directions in Psychological Science, 5, 58-61.

Daum, I., Schugens, M.M., Ackerman, H., Lutzenberger, W., Dichgans, & Birbaumer (1993). Classical conditioning after cerebellar lesions in humans. Behavioral Neuroscience, 107, 748-756.

Thompson, R.F., & Krupa, D.J. (1994). Organization of memory traces in the mammalian brain. Annual Review of Neuroscience, 17, 519-549.

Topka, H., Valls-Sole, J., Massaquoi, S.G., & Hallett, M. (1993). Deficit in classical conditioning in patients with cerebellar degeneration. Brain, 116, 961-969.

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