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Conditioning stirs 'synaptic memory.' (activity of hippocampus cells in the brain)

Conditioning stirs 'synaptic memory'

The hippocampus, a small bundle of cells deep in the brain, plays an important role in making the learned associations that characterize classical conditioning. When rabbits, for example, are simultaneously presented with a tone and an air puff aimed at the eye, the activity of pyramidal cells in this brain region increases before the animals learn to blink their eyes in response to the tone alone; pyramidal cell activity does not increase when the air puff and tone are presented separately (SN: 12/10/83, p. 380).

A similar type of conditioning has now been observed in rats, in the synapses that transmit nerve impulses to the same hippocampal cells. Since there is a form of "synaptic memory" in the hippocampus, say Stephen R. Kelso and Thomas H. Brown of the Beckman Research Institute of the City of Hope in Duarte, Calif., it may mediate simple types of learned associations. Learned associations involving more than one conditioning stimulus can be used with the synapses to see if cellular changes run parallel to similarly produced behavioral responses, they report in the April 4 SCIENCE.

Kelso and Brown obtained 14 hippocampal slices from 10 rats. In each slice, one of two nerve fibers feeding into the same synapse was weakly stimulated with an electrode and electrical activity in the synapse was measured. This stimulation was then paired with stronger electrical pulses delivered at the same time by another electrode placed in the same region. Electrical activity in the synapses in response to weak stimulation alone increased markedly 12 to 16 minutes after the pairing. If strong stimulation occurred just before or after weak stimulation, synaptic activity was not enhanced later.

It remains to be seen, say the researchers, whether hippocampal synapses in complex neuronal networks respond to conditioning sequences.
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Author:Bower, Bruce
Publication:Science News
Date:Apr 5, 1986
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