When and How Does the Auditory Cortex Influence Subcortical Auditory Structures? New Insights About the Roles of Descending Cortical Projections

Abstract

For decades, the corticofugal descending projections have been anatomically well described but their functional role remains a puzzling question. In this review, we will first describe the contributions of neuronal networks in representing communication sounds in various types of degraded acoustic conditions from the cochlear nucleus to the primary and secondary auditory cortex. In such situations, the discrimination abilities of collicular and thalamic neurons are clearly better than those of cortical neurons although the latter remain very little affected by degraded acoustic conditions. Second, we will report the functional effects resulting from activating or inactivating corticofugal projections on functional properties of subcortical neurons. In general, modest effects have been observed in anesthetized and in awake, passively listening, animals. In contrast, in behavioral tasks including challenging conditions, behavioral performance was severely reduced by removing or transiently silencing the corticofugal descending projections. This suggests that the discriminative abilities of subcortical neurons may be sufficient in many acoustic situations. It is only in particularly challenging situations, either due to the task difficulties and/or to the degraded acoustic conditions that the corticofugal descending connections bring additional abilities. Here, we propose that it is both the top-down influences from the prefrontal cortex, and those from the neuromodulatory systems, which allow the cortical descending projections to impact behavioral performance in reshaping the functional circuitry of subcortical structures. We aim at proposing potential scenarios to explain how, and under which circumstances, these projections impact on subcortical processing and on behavioral responses.

Listening loops and the adapting auditory brain

“…One difficulty in studying cortico-subcortical loops has been the sampling and targeting of, not only deep-sitting neurons, but also those specifically involved in the loop. Thanks to the development of genetic tools, combined with the creation of manipulation tools, we can now opto- and chemo-genetically target deep and superficial cells specifically involved in cortico-subcortical interactions in awake rodents ( Clayton et al, 2021 ; Souffi et al, 2021 ). The use of the newly developed large-scale high-density recording probes ( Jun et al, 2017 ) allows to record activity from deep and superficial neurons simultaneously across structures ( Kleinfeld et al, 2019 ).…”

Brainstem Auditory Physiology in Children with Listening Difficulties

“…Because the ABR and MEMR measures we employed here did not involve active listening to natural speech in noise, it seems unlikely that such downward control mechanisms were operational. Rather, the shorter latency and steeper growth curves in the LiD group may reflect poorer function of the corticofugal suppressive control networks (Souffi et al, 2021) having further downstream influences on brainstem ABR Waves III and V, and the MEMR. We are currently in the process of analyzing active speech-evoked and passive resting state MRI in these same children and will evaluate this hypothesis regarding functional connectivity of the frontal regions, primary auditory cortex, and auditory thalamus.…”

Instant improvement in monaural spatial hearing abilities through cognitive feedback

“…The presented model displays the multidisciplinary aspects of the presented work. The contribution of top-down processing in spatial hearing is important, although not yet fully understood (Souffi et al 2021). Studying "cognitive feedback" in this field of research is complex and there is still a lot to gain, since deep knowledge in psychology, metacognition (Flavell 1979;Dunlosky and Hertzog 2000), neuroscience and audiology is needed to really understand which factors are crucial in training sound localization abilities.…”