HEARING MORE THAN SOUND: ELECTROPHYSIOLOGICAL CHARACTERIZATION OF MULTISENSORY NEURONS IN THE AUDITORY MIDBRAIN USING IN-VIVO WHOLE CELL RECORDINGS

The inferior colliculus (IC) is a midbrain nucleus playing a major role in the auditory pathway. Its multisensory region, the lateral cortex (LCIC), was shown to receive inputs from somatosensory regions such as the somatosensory cortex and the dorsal column nuclei. The function of those projections is still largely unclear, especially on the single cell level. Here we wanted to investigate the effects of somatosensory stimulation and the interaction with simultaneous auditory stimulation within a single neuron. Thus, we conducted in vivo whole cell recordings in the LCIC of anesthetized mice to characterize the intrinsic electrophysiological properties of the neurons as well as their subthreshold responses to auditory, somatosensory and multisensory stimuli. Auditory stimuli were delivered using a close-field speaker. Somatosensory stimulation was delivered to the hind-paw via a custom device. Preliminary data suggested that all recorded neurons showed at least subthreshold responses to sound stimulation (excitatory, inhibitory or mixed), and approximately half of the recorded neurons showed at least subthreshold responses to somatosensory stimulation. Responses to pressure step stimulation can be subdivided into onset depolarization, offset depolarization and onset hyperpolarization. In a subset of somatosensory-responsive neurons, vibratory stimulation alone was enough to drive action potentials (APs), while simultaneous auditory stimuli reduced the amplitude of vibratory excitatory postsynaptic potentials and suppressed vibration-evoked APs. These findings suggest a heterogeneous multisensory neuronal population present within the IC. Ongoing experiments aim to explore the underlying cell physiological and circuit mechanisms of the observed multisensory interaction within these neuronal populations.