Processing of low-probability sounds by cortical neurons

Abstract

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.

Stimulus-specific adaptation, habituation and change detection in the gaze control system

“…Two major types of adaptations have been described in the literature: one is the non-specific adaptation that depends on the activation history of the neuron more than on specific features of the stimulus (Calford and Semple 1995;Brosch and Schreiner 1997;McAlpine et al 2000;Ingham and McAlpine 2004;Furukawa et al 2005;Wehr and Zador 2005;Gutfreund and Knudsen 2006); the other, a higher level adaptation, is stimulus-specific adaptation (SSA), an adaptation to the history of the stimulus rather than to the activity of the neuron (Ulanovsky et al 2003(Ulanovsky et al , 2004. To distinguish SSA from non-specific adaptation, several stimulation paradigms have been used (Fig.…”

“…1). Therefore, this phenomenon has been suggested as a single-unit neural correlate of the detection of unexpected stimuli (i.e., change detection, sometimes known as novelty detection; Ulanovsky et al 2003;Perez-Gonzalez et al 2005;Malmierca et al 2009). …”

“…Detailed characterization of SSA in the auditory system revealed that it is highly sensitive to minute deviations from the standard frequency. Neurons have been found to respond significantly more strongly to stimuli that are deviant from the standard by a frequency difference < as small as 0.1 % (Ulanovsky et al 2003). Moreover, it was shown that this adaptation has several time scales ranging from sub-seconds to tens of seconds (Ulanovsky et al 2004).…”

“…The last stimulus is salient because just like the sound of the door knob, it represents a stimulus that is out of order in time; a tone is heard during the time in which a broadband noise is expected, therefore this type of saliency will be referred to here as temporal saliency. Both temporal and spatial saliency are perceptually privileged; they give rise to attentional capture (Tiitinen et al 1994;Posner 1980), enhanced autonomic responses (Weisbard and Graham 1971;Bala and Takahashi 2000), and enhanced neural responses (Ulanovsky et al 2003;Reches and Gutfreund 2008;Naatanen 1995;Gottlieb et al 1998). Given these similarities in the outcome, it is likely that the neural mechanisms for mapping spatial saliency overlap with the neural mechanisms for mapping temporal saliency.…”

Context Effects in the Discriminability of Spatial Cues

“…Neural responses to frequency (Ulanovsky et al 2003), intensity (Dean et al 2005), or ITD (Malone et al 2002;Furukawa et al 2005) have all been shown to depend on stimulus history. Recently, this has been termed "adaptive coding"; adaptive coding designates any type of change in the neural activity (not only a reduction in firing rate) that results in a more efficient encoding of the stimuli (e.g., see Dean et al 2005 for evidence of adaptive coding of intensity in the auditory modality and Fairhall et al 2001 for adaptive coding in the visual modality).…”