Learning-related population dynamics in the auditory thalamus

Abstract

16Learning to associate sensory stimuli with a chosen action has been classically attributed 17 to the cortex. Whether the thalamus, considered mainly as an upstream area relative to 18 cortex, encodes learning-related information is still largely unknown. We studied learning-19 related activity in the dorsal and medial regions of the medial geniculate body (MGB), part 20 of the non-lemniscal auditory pathway. Using fiber photometry, we continuously imaged 21 population calcium dynamics as mice learned a go/no-go auditory discrimination task. The 22MGB was tuned to frequency shortly after stimulus onset and responded to cognitive 23 features like the choice of the mouse several hundred milliseconds later. Encoding of 24 choice in the MGB increased with learning, and was highly correlated with the learning 25 curves of the mice. MGB also encoded motor parameters of the mouse during the task. 26These results provide evidence that the MGB encodes task-motor-and learning-related 27 information. 28 29 78MGB population responses to sounds as mice learned a go/no-go auditory discrimination 79 task. We find learning-related modulations in the MGB, and a particularly strong 80 modulation to choice signals. 81 82 5 Results 83Calcium imaging from the MGB along learning 84 To study learning-related changes in the MGB we first injected AAV-GCaMP6f into the 85 MGB of C57BL/6 mice and implanted a 400 µm optical fiber directly above the injection 86 site. After a week of handling and habituation to head-fixation, we trained mice on a go/no-87 go auditory discrimination task. Each trial started with a visual start cue (orange LED; 88 duration 0.1 s; 2 seconds before stimulus onset) followed by an auditory stimulus, either a 89 go or a no-go pure tone sound ( Fig. 1A; duration 1 second; sounds separated by 0.5 octave; 90 mostly 10 kHz for go and 7.1 kHz for no-go; Methods). After stimulus offset, we counted 91 licks in a virtual response window of 3 seconds. Licking in response to the go sound were 92 counted as 'hit' trials and rewarded with a drop of water. Withholding licking in response 93 to the no-go sound were counted as correct rejection trials (CR), and were not punished or 94 reinforced. Licking in response to the no-go sound were counted as false alarm trials (FA) 95 that were followed by a mild punishment of white noise (duration 3 seconds). Withholding 96 licking for the go sound were counted as Miss trials, and were not punished. As mice 97 learned to discriminate between the two sounds we continuously imaged population 98 responses in the MGB in addition to monitoring their body movements during the task (Fig. 99 1B). We first imaged six mice across learning. The fiber tips of the six mice were 100 reconstructed to the higher-order regions of the MGB (Fig. 1C; MGBd and MGBm, 101 grouped as MGB for simplicity). Mice learned the task within 1200-2000 trials as assessed 102 by d' (defined as d' = Z(Hit/(Hit+Miss)) -Z(FA/(FA+CR) where Z denotes the inverse of 103 the cumulative distribution function; learning thres...

Sparse Coding in Temporal Association Cortex Improves Complex Sound Discriminability

“…TeA as a high-order auditory processing station Previous work studying higher-order sensory cortices involved characterization of receptive fields, identification of neuronal feature selectivity profiles, and examination of activity during task engagement (Marshel et al, 2011;Andermann et al, 2011;Elgueda et al, 2019;Gilad et al, 2020). Here, we studied auditory responses in passively listening mice, and identified two distinct features of FM responses in TeA, higher selectivity to FM direction (Fig.…”

Single cell plasticity and population coding stability in auditory thalamus upon associative learning

“…Taken together, our data indicates that auditory thalamus is ideally positioned to exhibit a complex role in guiding neuronal plasticity and valence assignment during associative learning that goes beyond the classical role of auditory processing and response potentiation during conditioning and potentially extrapolates to a broad set of behavioural functions (Gilad et al, 2020). Delineating the neural circuit mechanisms that underlie these highly dynamic representations of uni-and multisensory stimuli in MGB and their experience-dependent plasticity will open new avenues to understand the role of early, pre-cortical sensory relays like auditory thalamus in the formation of sensory percepts and memories that mediate complex behaviours.…”