Affiliation:
1. Division of Biology 216-76, California Institute of Technology, Pasadena, CA 91125, USA.
Abstract
Examples of multiplication by neurons or neural circuits are scarce, although many computational models use this basic operation. The owl's auditory system computes interaural time (ITD) and level (ILD) differences to create a two-dimensional map of auditory space. Space-specific neurons are selective for combinations of ITD and ILD, which define, respectively, the horizontal and vertical dimensions of their receptive fields. A multiplication of separate postsynaptic potentials tuned to ITD and ILD, rather than an addition, can account for the subthreshold responses of these neurons to ITD-ILD pairs. Other nonlinear processes improve the spatial tuning of the spike output and reduce the fit to the multiplicative model.
Publisher
American Association for the Advancement of Science (AAAS)
Reference25 articles.
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5. Data were obtained from 14 adult barn owls (Tyto alba) of both sexes. Owls were anesthetized by initial intramuscular injections of ketamine hydrochloride (25 mg/kg; Ketaset Fort Dodge) and diazepam (1.3 mg/kg; Western Medical Supply Phoenix AZ). Sharp glass electrodes filled with 2% neurobiotin in 2 M potassium acetate (pH 7.4) were advanced under visual control through a hole made on the bony cap containing the optic lobe. In all experiments acoustic stimuli broadband noise 100 ms in duration 30 dB above threshold were delivered by an earphone assembly consisting of a Knowles ED-1914 receiver as a sound source a Knowles BF-1743 damped coupling assembly for smoothing the frequency response of the receiver and a calibrated Knowles 1939 microphone for monitoring sound pressure levels in the ear canal. Neural signals were amplified with an Axoclamp-2A intracellular amplifier digitized and stored by a computer at a sampling rate of 24 kHz. To visualize and measure synaptic potentials we removed spikes using a median filter method (6). For more detailed methods see (7).
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