Tactile perception and memory in rats and humans: task and species differences within a general framework

Perceptual memories are the storage of our experiences; they are the basis for understanding the external world and guiding our decisions. Despite fast-paced research in the field, behavioural and cognitive constructs tend to be custom built around the investigators’ preferred task, and general principles across tasks seem to be missing. To address these issues, alongside psychophysical experiments, I aimed to build a computational model comprised of interconnected functional units, each performing a specific task-independent operation; the interaction between units and the readout of the system is controlled in a top-down mechanism, depending on goal-oriented requirements. I also aimed to relate this model to neuronal activity in two cortical regions, which are believed to be part of a network involved in perceptual decision making. Two groups of subjects, rats and humans, performed each of two different tasks requiring the elaboration of vibrotactile stimuli: (I) a categorization task, where a single stimulus must be judged (“strong” or “weak”) according to an implicit boundary, and (II) a delayed comparison task, where two stimuli are delivered in each trial, the first of which must be stored in short-term memory to be compared to the second. The results show that several aspects of trial history, such as recent stimuli and recent choice outcomes, factor into the choice of the current trial. Neuronal recordings from prefrontal and posterior parietal cortices, performed in rats executing both tasks, revealed that cortical activity accounted for decisional variables and past trials’ stimuli and choices, correlating with task performance and trial history, as emerged from behavioural results. These finding extend a previous model, thus helping to account for perceptual memory in a task-general manner.