Neuronal Models of Cognitive Functions Associated with the Prefrontal Cortex

Summary

Understanding the neural bases of cognition has become a scientifically tractable problem, and neurally plausible models are proposed to establish a causal link between biological structure and cognitive function. To this end, levels of organization have to be defined within the functional architecture of neuronal systems. Transitions from any one of these interacting levels to the next are viewed in an evolutionary perspective. They are assumed to involve:

• 1. the production of multiple transient variations and

• 2. the selection of some of them by higher levels via the interaction with the outside world.

The time scale of these “evolutions” is expected to differ from one level to the other. In the course of development and in the adult, this internal evolution is epigenetic and does not require alteration of the structure of the genome. A selective stabilization (and elimination) of synaptic connections by spontaneous and/or evoked activity in developing neuronal networks is postulated to contribute to the shaping of the adult connectivity within an envelope of genetically encoded forms. At a higher level, models of mental representations, as states of activity of defined populations of neurons, are suggested and their storage is viewed as a process of selection among variable and transient “pre-representations”. Models are presented which can perform the delayed response task or the Wisconsin card sorting test and cognitive functions such as short-term memory, reasoning and handling of temporal sequences. Implementations of these mechanisms at the cellular and molecular levels are proposed. Finally, speculations are offered about plausible neuronal models and selectionist implementations of intentions.