The processing of informationally relevant signals in the cochlea

Differential conditioning of associative synaptic enhancement in hippocampal brain slices

An electrophysiological stimulation paradigm similar to one that produces Pavlovian conditioning was applied to synaptic inputs to pyramidal neurons of hippocampal brain slices. Persistent synaptic enhancement was induced in one of two weak synaptic inputs by pairing high-frequency electrical stimulation of the weak input with stimulation of a third, stronger input to the same region. Forward (temporally overlapping) but not backward (temporally separate) pairings caused this enhancement. Thus hippocampal synapses in vitro can undergo the conditional and selective type of associative modification that could provide the substrate for some of the mnemonic functions in which the hippocampus is thought to participate.

The transfer function of the cochlea

A sinusoidal signal is generally considered the simplest auditory signal. It is, indeed, a simple signal. However, it does not follow that a complex analysing device, like the cochlea, should treat a simple signal in a simple way. Indeed, a simple signal may appear to be complex when viewed from the standpoint of the device considered. Such an observation becomes cogent when one is attempting to discover the analysing capabilities of a device such as the cochlea, which appears designed to handle signals more complex than a sinusoid or multiple sinusoids.