Processing of low-probability sounds by cortical neurons


The ability to detect rare auditory events can be critical for survival. We report here that neurons in cat primary auditory cortex (A1) responded more strongly to a rarely presented sound than to the same sound when it was common. For the rare stimuli, we used both frequency and amplitude deviants. Moreover, some A1 neurons showed hyperacuity for frequency deviants—a frequency resolution one order of magnitude better than receptive field widths in A1. In contrast, auditory thalamic neurons were insensitive to the probability of frequency deviants. These phenomena resulted from stimulus-specific adaptation in A1, which may be a single-neuron correlate of an extensively studied cortical potential—mismatch negativity—that is evoked by rare sounds. Our results thus indicate that A1 neurons, in addition to processing the acoustic features of sounds, may also be involved in sensory memory and novelty detection.

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Figure 1: Stimuli, and examples of single-neuron responses in A1.
Figure 2: Population analysis for A1 neurons.
Figure 3: Discriminability of frequency by A1 neurons, expressed as percentage correct.
Figure 4: Additional properties of cortical SSA.
Figure 5: Responses of neurons in the auditory thalamus (MGB) do not show SSA for 90/10%, Δf = 0.10.


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We thank G. Morris and G. Chechik for critical reading of the manuscript, and G. Karmos, I. Winkler, L. Deouell, H. Pratt, S. Bentin, S. Marom and M. Ahissar for stimulating discussions on the SSA–MMN comparison. This work was supported by a Human Frontiers Science Program grant to I.N. and a Horowitz Foundation predoctoral fellowship to N.U.

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Correspondence to Israel Nelken.

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Ulanovsky, N., Las, L. & Nelken, I. Processing of low-probability sounds by cortical neurons. Nat Neurosci 6, 391–398 (2003).

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