SUMMARY Neurons in visual, somatosensory, and auditory cortex can respond to the termination as well as the onset of a sensory stimulus. In auditory cortex, these off responses may underlie the ability of the auditory system to use sound offsets as cues for perceptual grouping. Off responses have been widely proposed to arise from postinhibitory rebound, but this hypothesis has never been directly tested. We used in vivo whole-cell recordings to measure the synaptic inhibition evoked by sound onset. We find that inhibition is invariably transient, indicating that off responses are not caused by post-inhibitory rebound in auditory cortical neurons. Instead, on and off responses appear to be driven by distinct sets of synapses, because they have distinct frequency tuning and different excitatory-inhibitory balance. Furthermore, an on-on sequence causes complete forward suppression, whereas an off-on sequence causes no suppression at all. We conclude that on and off responses are driven by largely nonoverlapping sets of synaptic inputs.

Sensory deafferentation results in rapid shifts in the receptive fields of cortical neurons, but the synaptic mechanisms underlying these changes remain unknown. The rapidity of these shifts has led to the suggestion that subthreshold inputs may be unmasked by a selective loss of inhibition. To study this, we used in vivo whole cell recordings to directly measure tone-evoked excitatory and inhibitory synaptic inputs in auditory cortical neurons before and after acoustic trauma. Here we report that acute acoustic trauma disrupted the balance of excitation and inhibition by selectively increasing and reducing the strength of inhibition at different positions within the receptive field. Inhibition was abolished for frequencies far below the trauma-tone frequency but was markedly enhanced near the edges of the region of elevated peripheral threshold. These changes occurred for relatively high-level tones. These changes in inhibition led to an expansion of receptive fields but not by a simple unmasking process. Rather, membrane potential responses were delayed and prolonged throughout the receptive field by distinct interactions between synaptic excitation and inhibition. Far below the trauma-tone frequency, decreased inhibition combined with prolonged excitation led to increased responses. Near the edges of the region of elevated peripheral threshold, increased inhibition served to delay rather than abolish responses, which were driven by prolonged excitation. These results show that the rapid receptive field shifts caused by acoustic trauma are caused by distinct mechanisms at different positions within the receptive field, which depend on differential disruption of excitation and inhibition.

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.

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With this year’s graduate student conferences hosted separately at the University of Calgary and Simon Fraser University, our goal was to encourage discussion and debate around the topic of crisis. The COVID-19 pandemic has been at the forefront of public attention; even forcing our respective conferences into the disembodied safety of virtual space. However, it is important to remember that COVID-19 is not the only crisis faced in recent years; the overdose crisis, crisis of the corporatization of universities, economic crisis, crisis of truth and misinformation, and the looming environmental threat of the Anthropocene, have been with us and will continue to be grappled with into the foreseeable future. Crises echo through the past to the present, such as those experienced by our Indigenous communities. They re-emerge, still to be grappled with and struggled against. As individuals and researchers, we may assume any number of these crises are out of scope or outside our area of expertise. We often fail to consider them. However, crises defy temporality and spatiality as easily as disciplinary borders; both squeezing and stretching, accelerating, and suspending notions of the like. The contributors of this special issue consider an array of crises as they collide with diverse fields and disciplines, encouraging us to reflect on how they intersect our own. Ultimately, we aspire to trouble the notion of crises themselves. Questioning our understanding and reapplying it where we had not previously considered. In these general ‘times of crisis,’ what counts as such? How is it communicated and miscommunicated? What are the effects on resilience, recovery, and possibility? Where can we seize opportunity following a crisis? The Chinese symbol for crisis is composed of two parts: opportunity and danger. Where the Simon Fraser University conference focused on resilience in a crisis, the University of Calgary conference expanded on potentials of opportunity. As invited editors to this special edition, we viewed contributors, not as tackling separate entities of the term ‘crisis,’ but instead, as a framework to building back stronger, seizing an opportunity, and practicing resiliency as we maneuver through this danger to a better future. As Zhang and Li (2018) have argued, it is in a co-creation of both sustainable and resilient development which can lead to assurances of overcoming and withholding a community’s vulnerabilities, or their potential crises. This development may use standards setting as an opportunity to ensure resiliency (Thompson, 1954), encouraging democratic participation for an equal seat at the table, and taking the lessons learned during a crisis to apply to a better future (Brundtland, 1987). In the field of communication, we are oftentimes stretched to an incohesive front based on the competing discourses of the canons of our field (Carey, 1997, 2009; Peters, 1999). The study of communications then is not a discipline, but a field of fields, perhaps a crisis of definition in our own knowledge community. In these competing views we see the beauty of this interdisciplinary and transdisciplinary research, as reflected in how graduate students across Canada thrive in their specializations. Emerging as a new group of scholars who, as the world was faced by crises all around, produced these articles in the pages which follow for this special edition; we as the invited editors see the ways in which graduate students practice resiliency in their work, seizing opportunities, and overcoming the crises which surround. 危机 Crisis.