| This thesis develops a mathematical model of cortical interactions responsible for various aspects of working memory, sequence learning, planning, and performance during cognitive information processing and sensory-motor control. The model explains and simulates cognitive data about immediate serial recall and immediate free recall, and sensory-motor data about the drawing of geometrical figures. Working memory encompasses the processes by which information about sequences of events can be temporarily stored, and thereby enable the brain to learn and remember them. The cortical areas that sub-serve these functions include the lateral prefrontal cortex, and the posterior and the medial parietal and temporal lobes. The model proposes a functional explanation of the laminar circuitry of the lateral prefrontal cortex, showing how the proposed circuitry and known connectivity with both sensory and motor systems enables it to play a role in the retention, processing and organized storage of multi-modal, temporally ordered items for voluntary behavior and conscious perception. The model's cognitive mechanisms propose how short-term item storage, learned grouping of sequential information into functionally linked chunks, resetting of item storage, and updating information from long-term memory occur. The model's motor mechanisms describe how real-time sequential rehearsal of simultaneously activated plans in a motor working memory occur, including the role of volition in enabling and coordinating variable-rate performance. The model's proposal about how variable-rate performance is controlled clarifies how sequences of learned motor actions can be anticipatorily timed, so that selection of the next action can begin at an appropriate time prior to current movement completion. Model explanations and simulations of cognitive data about immediate serial recall and free recall include: bowing of the serial position performance curves, error-type distributions, limited temporal extent for accurate recall, and list length effects. The model also provides explanations for cognitive effects related to: modulation of attention, temporal grouping, variable presentation rates, phonemic similarity, presentation of non-words, distracter tasks, modality, and word frequency/item familiarity and list strength. Finally, the model simulates neurophysiological data from the macaque prefrontal cortex obtained during sequential motor performance of geometrical figures. |
