MRI-assessed volume of cerebellum correlates with associative learning

Richard F. Thompson's cerebellar model of classical eyeblink conditioning h ighlights Purkinje cells in cerebellar cortex. and principal cells in the d eep cerebellar nucleus as the integrating cells for acquisition of conditio ned responses (CRs). CR acquisition is significantly slower in. rabbits wit h lesions to cerebellar cortex and in Purkinje cell-deficient mice that los e all cerebellar cortical Purkinje cells. Parkinje cells are the largest ne urons in the cerebellum and contribute significantly to cerebellar volume. Magnetic resonance imaging (MRI) was used to assess cerebellar volume in hu mans. Cerebellar volume was related to eyeblink conditioning (400-ms delay procedure) in 8 adults (21-35 years) and compared to 8 older adults (77-95 years) tested previously (Woodruff-Pak, Goldenberg, Downey-Lamb, Boyko, & L emieux, 2000). In the young adult sample, there was a high correlation betw een percentage of CRs in a session and cerebellar volume (corrected for tot al intracranial volume [TIV], r =.58, p =.066). There were statistically si gnificant age differences in cerebellar volume, t(14) = 8.96, p < .001, and percentage of CRs, t(14) = 3.85, p < .002, but no age difference in TIV. C ombining the young and older adult sample, the correlation between percenta ge of CRs and cerebellar volume (corrected for TIV) was .832 (p < .001). Ce rebellar volume showed age-related deficits likely due to Purkinje cell los s. Individual differences in classical eyeblink conditioning are associated with differences in cerebellar volume, supporting Thompson's model of a ce rebellar cortical role in facilitating this form of associative learning. ( C) 2001 Academic Press.