Laboratoire des Systèmes Perceptifs
Perceptual decision-making in detection and discrimination tasks results from a complex and subtle integration of sensory and contextual information. How task structure is learned and encoded in the brain is still an open question. In particular, stable large-scale recordings of brain activity appears to be technically challenging. As such, a complete understanding of the changes elicited in neural sensory maps during the course of learning is missing. Polley et al. showed that rats trained to attend frequency cues exhibited an expanded representation of the target frequency range at the level of the primary auditory cortex . These data suggest that enduring receptive field plasticity in the adult auditory cortex may be shaped by task-specific top-down feedbacks, interacting with bottom-up sensory inputs and reinforcement-based neuromodulator release. However, the time-course of these neural correlates still remains to be investigated, as it could provide crucial insight on how they precede or follow increases in performance. Moreover, different studies of plasticity in the visual, motor, and auditory systems indicate that representational maps are rather/also dynamically modulated, and that cortical cells in these systems can undergo rapid, task-dependent and context-specific changes of their receptive field properties during attentive behavior . How such changes occur across the whole auditory pathway (from midbrain to high-order auditory areas), and how gating modulates task-irrelevant sensory structures remains unclear.
We aim at tackling these two questions using functional UltraSound (fUS ) imaging in awake, behaving ferrets. This newly developed technique, based on Doppler effect to measure changes in blood flow, allows us to image brain activity on a large scale (1x2cm) at a high spatial (100µm) and temporal (down to the cardiac cycle) resolution. Finally, through precise stereotaxic coordinates and image correlation techniques, we can image the same brain slice over days. Our experimental setup thus provides a perfect framework for imaging modifications of tonotopic maps and stimulus processing over days and during learning, or even more dynamically across changing brain states. The goal of this internship is to acquire long-term spatio-temporal patterns of brain activation in multiple brain areas (from subcortical sensory structures to possibly frontal cortex) while ferrets are learning behavioral tasks, and then to identify possible changes in evoked response properties and functional correlation. This involves a combination of experimental skills (behavioral training, ultrasound recordings) coupled with data analysis. The internship can be conducted indiscriminately in French or English.
 D. B. Polley, “Perceptual Learning Directs Auditory Cortical Map Reorganization through Top-Down Influences,” Journal of Neuroscience, vol. 26, no. 18, pp. 4970–4982, 2006.
 J. Fritz, S. Shamma, M. Elhilali, and D. Klein, “Rapid task-related plasticity of spectrotemporal receptive fields in primary auditory cortex.,” Nature neuroscience, vol. 6, pp. 1216–1223, nov 2003.
 Bimbard, C., Demene, C. , Girard, C. , Radtke-Schuller, S., Shamma, S., Tanter*, M. & Boubenec*, Y. (2018). Multi-scale mapping along the auditory hierarchy using high-resolution functional UltraSound in the awake ferret. eLIFE. doi:10.7554/eLife.35028.001