Plenary Lecture

Plenary Lecture

The Role of the Cerebellum in Associative Memory is Control of the Oculomotor Expression of the Memory
but not its Storage

Professor I. Steele-Russell
Neuroscience & Experimental Therapeutics
College of Medicine
Texas A&M University System HSC
College Station, TX

The eye-blink reflex in the rabbit is currently regarded as an ideal animal model to study the neural mechanisms of associative memory. This claim rests on three main assumptions, which are: (a) all the sensory inputs and motor outputs are under total experimental control, (b) the learning is completely isomorphic with the eye blink response, and (c) the memory storage of this learning is mediated by the cerebellar cortex. It will be argued that all of these assumptions are highly questionable.
(a) Input control: Recent research indicates that selective attention plays a major role in determining sensory processing in eye blink conditioning (Steele-Russell et al, 2006: Steele-Russell et al, 2007). Without control over the animal's selection of sensory channels it is not possible to restrict the learning to specific input pathways in the brain. For example, in visual Pavlovian conditioning, it is critical to control for albedo, regional flux, shift signals etc, during learning. Failure to do so can result in the activation of multiple pathways, i.e. pattern or brightness channels. In addition pathways including both auditory and tactile channels can be involved - all of which converge on the final common path of the oculomotor blink response. The failure to control for selective attention is the reason why the nature of the sensory inputs contributing to the learning remain unknown.
(b) Response invariance: Recent evidence has shown that the eye blink conditioning in the Pavlovian stock, when subsequently tested in a different free environment, is expressed by very different responses than a simple eye blink reflex (Castiglioni et al, 2009). These findings suggest that the conditioning does not involve simple reflex response learning. They indicate that the learning involves the acquisition of a new meaning to the sensory signal, which can produce different response patterns in different situations.
(c) Cerebellar memory storage: This position was tested by comparing eye blink conditioning in both normal and chiasma sectioned rabbits. Midline section of the optic chiasma results in disconnection of the direct retinal projections via the brainstem to the cerebellar oculomotor control system. Thus by comparing both normal and chiasma animals it is possible to determine the dependence/independence of conditioning on the motor expression of the eye blink response during training. Oculomotor tests showed a complete lack of eye-lid conditioning in chiasma sectioned rabbits. However the sensory tests of learning in these animals, revealed perfectly normal sensory recognition learning to the visual signal.
Conclusions: These findings establish that the critical element in conditioning is the cognitive learning of the change in the meaning of the sensory signal. Furthermore this learned information is totally independent of any cerebellar mechanisms.

Brief Biography of the Speaker:
Ian Steele-Russell is a full professor in the department of Psychiatry & Behavioral Science, the department of Neuroscience and experimental Therapeutics and the department of Veterinary Integrative Biomedical Sciences at Texas A & M University System Health Science center, USA. His areas of research are in visual neuroscience with a specific emphasis on cortical mechanisms of selective attention in visual perception and memory. He has authored or co/authored over 202 papers published in peer-reviewed journals or presented at scientific conferences. He contributed to the book The Structure and Function of the Cerebral Commissures edited by I Steele-Russell, MW van Hof, G. Berlucchi, 1979. He is the Founding Editor-in-Chief of the International Journal Behavioural Brain Research and has served on the editorial boards of several international journals in the neuroscience area, such as Physiology and Behavior, Brain Research Bulletin, Activitas Nervosa Superior, and Memory Research. He was a former President of the European Brain Behaviour Society from 1979-1982. He is currently head of the Visual Neuroscience Laboratory.

WSEAS Unifying the Science