Biomedical Engineering Reference
In-Depth Information
(stellate and basket cells). The large pear-shaped cell bodies of Purkinje cells are
aligned side by side in a single layer, known as the Purkinje cell layer. The ex-
tensive dendritic tree of a Purkinje cell extends into the molecular layer in a sin-
gle plane. The granular layer is the innermost layer and primarily contains
densely packed, small granule cells as well as a few larger interneurons (Golgi
cells).
The cerebellar cortex receives afferent input from most parts of the periph-
eral and central nervous system. The most important afferent fibers consist of
mossy fibers and climbing fibers. Climbing fibers originate solely from the infe-
rior olive in the brain stem. Mossy fibers originate from different brain stem
nuclei and neurons in the spinal cord. The mossy fiber afferents terminate in the
granular cell layer. Mossy fiber contacts with dendrites of granule and Golgi
cells are known as cerebellar glomeruli. The mossy fibers alter the activity of the
Purkinje cell via the parallel fibers. Each Purkinje cell receives inputs from nu-
merous granule cells, and each granule cell collects inputs from several mossy
fibers. Climbing fibers directly contact the dendrites of the Purkinje cell. Each
Purkinje cell receives input from a single climbing fiber, and one climbing fiber
contacts 1 to 10 Purkinje cells.
The Purkinje cell is the only output neuron of the cerebellar cortex. Purkinje
cells have a GABAergic, inhibitory action on the cerebellar nuclear neurons.
Both mossy and climbing fiber afferents have an excitatory action on the Pur-
kinje cell. The excitatory input is modulated by inhibitory interneurons (stellate
and basket cells in the molecular layer, and Golgi cells in the granular layer).
2.
EXPERIMENTAL APPROACHES AND BEHAVIORAL DATA
2.1. Tests for Associative Processes
2.1.1. Eyeblink Conditioning
There are numerous studies that provide clear evidence for critical involve-
ment of cerebellar structures in classical conditioning of the eyeblink reflex. The
parts of the cerebellar cortex and cerebellar nuclei involved in eyeblink condi-
tioning have been assessed carefully in animal models. Animal lesion studies,
most in the rabbit, indicate that the ipsilateral interposed nucleus and Larsell
lobule H VI are of particular importance for acquiring conditioned responses
(for a review see (9,71,81)).
In addition to electrophysiological studies, functional brain imaging has
been the most widely used technique to study the involvement of structures in
behavior of humans. This is discussed in more detail in Part IV, chapter 5, by
Breiter, Gasic, and Makris (this volume). From several human lesion and func-
tional brain imaging studies there is evidence that the human cerebellum is also
