Level Dependence of Contextual Modulation in Auditory Cortex

Abstract

Scholl B, Gao X, Wehr M. Level dependence of contextual modulation in auditory cortex. J Neurophysiol 99: 1616 -1627, 2008. First published January 23, 2008doi:10.1152/jn.01172.2007. Responses of cortical neurons to sensory stimuli within their receptive fields can be profoundly altered by the stimulus context. In visual and somatosensory cortex, contextual interactions have been shown to change sign from facilitation to suppression depending on stimulus strength. Contextual modulation of high-contrast stimuli tends to be suppressive, but for low-contrast stimuli tends to be facilitative. This trade-off may optimize contextual integration by cortical cells and has been suggested to be a general feature of cortical processing, but it remains unknown whether a similar phenomenon occurs in auditory cortex. Here we used whole cell and single-unit recordings to investigate how contextual interactions in auditory cortical neurons depend on the relative intensity of masker and probe stimuli in a two-tone stimulus paradigm. We tested the hypothesis that relatively low-level probes should show facilitation, whereas relatively high-level probes should show suppression. We found that contextual interactions were primarily suppressive across all probe levels, and that relatively low-level probes were subject to stronger suppression than high-level probes. These results were virtually identical for spiking and subthreshold responses. This suggests that, unlike visual cortical neurons, auditory cortical neurons show maximal suppression rather than facilitation for relatively weak stimuli.

Long-Lasting Context Dependence Constrains Neural Encoding Models in Rodent Auditory Cortex

“…Sensory neurons typically have a dynamic range greatly exceeded by that of the sensory environment. The timescale of adaptation typically depends on stimulus statistics and the direction of the changes (Baccus and Meister 2002;David et al 2009;DeWeese and Zador 1998;Kvale and Schreiner 2004;Pienkowski and Eggermont 2009;Scholl et al 2008;Smirnakis et al 1997;Wehr and Zador 2005). In fact we found that differences in stimulus intensity and bandwidth had stronger and longer effects on the neuronal responses to the following stimuli than those in AM, FM, or other higher-order spectrotemporal modulations (Fig.…”

Plastic changes along auditory pathway during salicylate-induced ototoxicity: Hyperactivity and CF shifts

“…CF upshifts and downshifts emerged in the IC and became more pronounced in the AC. Such changes are likely mediated by diminished inhibition that allows the full range of spectral inputs to be expressed when the suppressive effects of lateral inhibition are removed (Salvi et al, 2007; Scholl et al, 2008; Wang et al, 2002a; Wang et al, 2002b; Wehr and Zador, 2003). …”

Contextual modulation of sound processing in the auditory cortex

“…The magnitude of forward suppression depends on the frequency and intensity of the masker, creating a suppressive area that matches the frequency response area (FRA) of the neuron, and decays at large delays between the probe and masker, approximately 250ms after masker onset [11,28,29]. The suppressive effect of the masker is released with increasing probe intensities, suggesting a competitive interaction between excitatory responses to the probe, and delayed inhibitory responses to the masker (Figure 2B) [30]. Whole-cell recordings show that inhibitory conductances elicited from the masker last only 50 to 100ms, indicating the involvement GABA-mediated synaptic inhibition at short timescales, but also that long-term synaptic depression may underlie suppression observed at longer delays [32].…”

“…Note the suppression of spiking in response to the probe when preceded by masker tones that elicited strong responses, such that forward suppression roughly resembles the FRA of the neuron. Figure adapted from Scholl et al, 2008 [30]. …”