Research projects

This project aims to test if the principles of predictive coding occur at the neuronal level, at different stages of the auditory hierarchy and evaluate how they are impaired in aging and Alzheimer´s disease or affected by hearing loss. So far we have trained two groups of rats to discriminate deviant tones embedded in an oddball paradigm to assess the influence of attention on neuronal mismatch. Animals were exposed to different variations of an oddball paradigm changing the standard/deviant probability (70/30% and 90/10%), the interstimulus interval (1.5, 2 and 4 seconds) and the frequency contrast between the standard and the deviant stimuli (0.5, 0.75, 1.00, 1.25 octaves). Finally, animals were tested with a variation of the oddball paradigm (many deviants task) where frequency contrast between standard and deviant was randomly varied from 9 possibilities. To determine the animal’s ability to recognize deviant tones intermingled in the paradigms presented, we calculated the d’ discrimination index, where larger d’ values indicate better discrimination ability. Results demonstrate that all animals show a d’>1 when varying the interstimulus interval but no significant differences occurred across cases. In the oddball sequence task, when varying the frequency contrast there is a progressively increase in d’ as a function of as the contrast increases, in both groups, but performance reach a steady state level when the contrast reaches 1.00-1.25 octaves. Similarly, when the probability of occurrence is changed from 90/10 to 70/30%, a significant decrease in the d’ values occur for all. Finally, d’ is similar when the classical oddball paradigm and the many deviants task are tested. The percentage of responses for each deviant frequency is similar for all contrasts except for the ones that are closer to the standard frequency, where it’s lower and the latency of the responses for each deviant frequency is constant.