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Abstract:
Our understanding of information processing in nerve nets
has been modified by the concept of graded signal
transmission. Descriptions of non-spiking interneurons in
insects, and the demonstration of graded synaptic
transmision have contributed to this development. In the fly
visual nervous system, second and higher order interneurones
are known, which apparently do not produce action
potentials. We show here that at least eight individually
identifiable movement-sensitive cells, which have the
characteristic properties of non-spiking
interneurones, will generate spikes with imposed
hyperpolarisation. Their graded mode of operation is due to
maintained refractoriness. This applies selectively to
neurones, which belong to either of two anatomically,
and physiologically distinct classes. Ohter cell types in
the same preparation generate spikes spontaneously.
