Contextualised auditory processing in subcortical circuits

Sensory events are always embedded within a specific context and it is well established that their representations in sensory cortex are highly context dependent. Cortical responses are modulated by motor commands, other sensory cues, cognitive demands, and the statistics of the environment. However, some of these contextual influences found in cortex could be inherited from subcortical processing levels.

In recent years, the thalamus has received renewed interest, and several studies have suggested that sensory processing at this level may also be context dependent, often guided by cortico-thalamic feedback. However, the range of contextual influences on thalamus and other subcortical structures is poorly understood, as are the circuits needed to implement such contextualisation of subcortical sensory processing.

In my talk I will present results from my DPhil work where I have asked whether two fundamental aspects of context-dependent processing found in the auditory cortex – multisensory integration and adaptation to stimulus statistics – also occur subcortically, and what the underlying neural circuits might be.

Firstly, I will demonstrate using mice that the auditory thalamus as a whole is influenced by somatosensory information in diverse, but pathway-specific ways, with primary auditory cortex inheriting signals from the thalamus that are divisively scaled by somatosensory whisker stimulation. I will show that this is dependent on a primary somatosensory corticofugal projection and implemented via neurons in the higher order auditory midbrain receiving input from somatosensory cortex and providing somatosensory inhibitory signals to auditory thalamus. Furthermore, I will demonstrate the presence of a parallel direct cortico-thalamic pathway from primary somatosensory cortex to the medial sector of auditory thalamus, which is capable of driving spiking activity and facilitating auditory responses.

Secondly, I will show that auditory contrast adaptation is present in the auditory midbrain and thalamus, as well as the cortex, and that this computation is gradually stabilised with each ascending processing level, with implications for perceptual acuity. Furthermore, I find that contrast adaptation in subcortical structures can be implemented without the need for corticofugal feedback, revealing an extensive, purely subcortical role in the implementation of this important feature of sensory processing.

Together, these results reveal a previously underappreciated role for subcortical structures in implementing several contextual neural principles often assumed to require cortical circuitry