Journal: bioRxiv

Article Title: Visual modulation of spectrotemporal receptive fields in mouse auditory cortex

doi: 10.1101/2021.08.06.455445

Figure Lengend Snippet: Single unit recording and audiovisual stimulation in awake mouse auditory cortex. ( A ) Mice were head fixed atop a spherical treadmill. A headbar window provided access to primary auditory cortex (A1) of the right hemisphere for extracellular recording with translaminar probes. Sounds were presented to the contralateral ear through an electrostatic speaker and visual stimuli were presented via a monitor centered in front of subjects at 25 cm distance. ( B ) Coronal mouse brain section with magnification of A1 and linear multichannel electrode arrays (64-channels, 20μm spacing) used to simultaneously record neuronal activity across all cortical layers. ( C ) Auditory cortical depth estimation. ( a ) Multiunit responses evoked by search stimuli (e.g., click trains, noise bursts, pure tones) were used to guide visual demarcation of the span of responsive channels which served as an estimate of the putative cortical span and was used to assign a fractional depth value to each recorded neuron. Fractional responsive span was further divided into Superficial, Middle, and Deep bins. ( b–d ) Example multiunit responses from (b) the shallowest channel of the responsive span, (c) responsive channels from the middle of the probe, and (d) deepest channel of the responsive span. ( D ) Identification of putative excitatory and inhibitory neurons by waveform morphology clustering. ( a ) Example single-unit waveform (black line: median, gray shading: median absolute deviation) showing trough-peak delay calculation. ( b ) The distribution of trough-peak delay times was sharply bimodal, permitting straightforward identification of broad spiking (BS; putative excitatory) and narrow spiking (NS; putative inhibitory) neurons. BS and NS unit populations were further distinguished by differences in spontaneous firing rate. ( E ) Auditory and visual stimulation paradigm. ( a ) Auditory trials comprised non-repeating 15-s segments of a random double sweep (RDS) stimulus, comprising two continuously frequency-modulated pure tones which varied independently of one another between 4 and 64 kHz. Trials were separated by silent intertrial intervals (~4–9 s), permitting calculation of spontaneous firing rates. Sound onset firing rate responses were defined by a 100-ms window post-stimulus onset. Sustained firing rates were quantified within a window 200-ms post-stimulus onset to the end of the stimulus (15 s). Inset shows the example unit spike waveform (median ± MAD). ( b ) Audiovisual trials were identical to Auditory trials (including the same RDS segments) with the addition of a visual contrast modulated noise (CMN) stimulus. The CMN stimulus led and trailed the RDS stimulus by 2.5 s, permitting unambiguous assessment of visual onset and offset firing rate responses and allowing adaptation to the visual stimulus prior to sound onset. The auditory (RDS) and visual (CMN) stimuli were uncorrelated with each other. Auditory and Audiovisual trials were interleaved in pseudorandom order.

Article Snippet: The silicone elastomer filling the craniotomy was removed and a single shank, linear multichannel electrode array (Cambridge Neurotech) was slowly lowered into cortex using a motorized microdrive (FHC).

Techniques: Single-unit Recording, Activity Assay