Authors: Francesco Mannella, Vincenzo Fiore, Marco Mirolli, Gianluca Baldassarre
Topic and its relevance. Organisms have a brain that evolved to produce a behaviour that enhances their survival and reproductive chances. To do this, brain produces body movements (actions) in correspondence to sensations. More sophisticated organisms, as primates, need to learn to perform and appropriately select a large number of actions depending on the environmental conditions and current internal needs. A very complex hierarchical brain architecture underlies these processes. This architecture involves the production of dynamic movementes/actions (somatosensory cortex, primary motor cortex, dorsal basal ganglia, cerebellum), their selection (premotor cortex, dorsal/medial basal ganglia), their selection and sequencing based on the organism's goals (dorsolateral prefrontal cortex, supplementary motor cortex, medial basal ganglia), their selection at a higher level based on the organisms' ultimate motivations and needs (hypothalamus, amygdala, ventral basal ganglia, orbital and ventromedial prefrontal cortex). Habits involve the automatic triggering of actions in the presence of a particular external and internal context: they typically involve dorsal basal ganglia and premotor/primary cortex. Goal-directed behaviour involves the triggering of actions on the basis of internal motivations and goals: this typically involve amygdala, ventral/medial basal ganglia, and orbital and ventromedial prefrontal cortex. Although we have much evidence on these issues, we are still far from having a complete whole picture on these processes. The importance of this research resides in the fact that understanding these processes means understanding a large part of the whole brain functioning.
Questions and goals. What are the functions and mechanisms (i.e., architectural, functioning, and learning features) underlying goal-directed behaviour and habits? How are dynamic movement primitives and goals formed? How do habits form? How is goal-directed behaviour controlled by internal motivations and external context? What are the mechanisms of arbitration between goal-directed and habitual behaviour?
Methods. We investigate these issues through bio-constrained computational models. We start with the overall goal of accounting for specific psychbiology experiments, usually carried out with rats/mice, for example on: classical conditioning, second order conditioning, stress coping, instrumental conditioning, devaluation, Pavlovian to intrumental transfer, etc. We constrain the mechanisms of models on the basis of the known anatomy of brain and lesion experiments: we start from the macro-anatomy and then, when made necessary by the targeted behaviours and the refinement of the model, we specify the meso architecture (e.g., internal modules of basal ganglia, amygdala; specific areas of ventro-medial prefrontal cortex) and micro architecture (micro-anatomy and cell types of amygdala, basal ganglia, and cortex).
Results. This approach allows us to isolate sufficient hypotheses to account for the target behaviours and the related neuroscientific evidence in a coherent and comprehensive way. The high number of constraints imposed on the models at the behavioural and neuroscientific anatomical/functioning/learning levels also increase the ``probability of the necessity'' of the proposed hypotheses, i.e. that the models we propose capture what actually happens in brain. The models so proposed produce specific empirical predictions that can be tested with further empirical experiments: we have started collaborations with neuroscientists to test some predictions generated by our models.
Conclusions. Based on this integrated approach, we have formulated models that incorporate sufficient hythesis on the brain mechanisms that might underlies various behaviours studied in psychobiological experiments, e.g. various forms of classical conditioning, devaluation, stress coping experiments. These models produce predictions, and furnish comprehensive pictures often lacking in psyhchobiology and neuroscience, that foster and guide further empirical research on the issues.