Anti-Hebbian Learning - Evidence From Neuroethology

Evidence From Neuroethology

Neuroethological study has provided strong evidence for the existence of a system which adheres to an anti-Hebbian learning rule. Research on the mormyrid electric fish has demonstrated that the electrosensory lateral-line lobe (ELL) receives sensory input from momyromast receptors (elctroreceptive sensory organs) which utilize a self-generated electrical discharge (called an EOD; electric organ discharge) to extract information from the environment about objects in close proximity to the fish.

In addition to information from sensory receptors, the ELL receives a signal from the area of the brain responsible for initiating the electrical discharges, known as the EOD command nucleus. This efference copy diverges, transmitted through two separate pathways, before the signals converge along with electrosensory input on Purkinje-like Medium Ganglion cells in the ELL. These cells receive information through extensive apical dendritic projections from parallel fibers that signal the transmission of an order to release an EOD. These cells also receive information from neurons conveying electrosensory information.

Important to anti-Hebbian learning, the synapses between the parallel fibers and the apical dendrites of Medium Ganglion cells show a specific pattern of synaptic plasticity. Should activation of the dendrites by parallel fibers occur in a short time period preceding the initiation of a dendritic broad spike (an action potential which travels through the dendrites), the strength of the connection between the neurons at these synapses will be reduced. Activation by the parallel fibers in all other circumstances – including activation significantly preceding as well as any activation following the broad spike – will result in the strengthening of the synaptic connections