The Journal of Neuroscience, July 1, 2002, 22(13):5652-5658
From Postsynaptic Potentials to Spikes in the Genesis of Auditory
Spatial Receptive Fields
José Luis
Peña and
Masakazu
Konishi
Division of Biology, California Institute of Technology, Pasadena,
California 91125
Space-specific neurons in the owl's inferior colliculus respond
only to a sound coming from a particular direction, which is equivalent
to a specific combination of interaural time difference (ITD) and
interaural level difference (ILD). Comparison of subthreshold postsynaptic potentials (PSPs) and spike output for the same
neurons showed that receptive fields measured in PSPs were much larger than those measured in spikes in both ITD and ILD dimensions. Space-specific neurons fire more spikes for a particular ITD than for
its phase equivalents (ITD ± 1/F, where F is best frequency). This differential response was much less pronounced in PSPs. The two
sides of pyramid-shaped ILD curves were more symmetrical in spikes than
in PSPs. Furthermore, monaural stimuli that were ineffective in
eliciting spikes induced subthreshold PSPs. The main cause of these
changes between PSPs and spikes is thresholding. The spiking threshold
did not vary with the kind of acoustic stimuli presented. However, the
thresholds of sound-induced first spikes were lower than those of later
sound-induced and spontaneous spikes. This change in threshold may
account for the sharpening of ITD selectivity during the stimulus.
Large changes in receptive fields across single neurons are not unique
to the owl's space-specific neurons but occur in mammalian visual and
somatosensory cortices, suggesting the existence of general principles
in the formation of receptive fields in high-order neurons.
Key words:
receptive fields; maps of space; sound localization; auditory system; barn owl; inferior colliculus
Copyright © 2002 Society for Neuroscience 0270-6474/02/22135652-07$05.00/0
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