PARALLELS IN AGE-RELATED CHANGES IN LEARNING AND THE CEREBELLUM
D. S. Woodruff-Pak
Temple University, Department of Psychology, 1701 North 13th Street,
Philadelphia, PA 19122
Age-related changes in the cerebellum appear relatively early in
mammals, and a cerebellar role has been demonstrated for many forms of
cognition including associative learning, language, visual-spatial
ability, and working memory. However, associations between age-related
changes in the cerebellum and cognition are rarely investigated.
Purkinje cells in cerebellar cortex and principal cells in deep
cerebellar nuclei have been identified as the central integrating cells
for a form of associative learning called classical eyeblink
conditioning. Acquisition of conditioned eyeblink responses is
significantly slower in rabbits with lesions to cerebellar cortex and
in Purkinje cell deficient mice that loose all cerebellar cortical
Purkinje cells. Correlations between Purkinje cell number and
acquisition of conditioned responses (CRs) in rabbits are high and
statistically significant, even when the age range is limited to young
rabbits. In humans, significant age differences in MRI-assessed
cerebellar volume appear in the age-decade of the 50s. Purkinje cells
are the largest neurons in the cerebellum and contribute significantly
to cerebellar volume. MRI-assessed cerebellar volume (corrected for
total intracranial volume, TIV) was related to eyeblink conditioning
(400 ms delay procedure) in older adults ranging in the age range of 77
to 95 years (r = 0.81, p < 0.01) and in young adults in the age range
of 21 to 35 years (r = 0.58, p = 0.066). Between these two age groups
there were statistically significant age differences in cerebellar
volume (t(14) = 8.96; p < 0.001) and percentage of CRs (t(14) = 3.85; p
< 0.002), but no age difference in TIV. Combining the young and older
adult sample, the correlation between percentage of CRs and cerebellar
volume (corrected for TIV) was 0.832 (p < 0.001). Cerebellar volume
showed age-related deficits likely due to Purkinje cell loss.
Individual differences in classical eyeblink conditioning are
associated with differences in cerebellar volume indicating a
cerebellar cortical role in facilitating this form of associative
learning. Supported by grants from the Alzheimer's Association
(IIRG-99-1690) and the Harry A. Stern Family Foundation.
Key words:
Purkinje cells, classical conditioning, magnetic resonance imaging (MRI)
Problems or questions regarding this site should be directed to
webmaster@americanaging.org