Transcript Slide 1
Background • The physiology of the cerebral cortex is organized in hierarchical manner. • The prefrontal cortex (PFC) constitutes the highest level of the cortical hierarchy dedicated to the representation and execution of actions. • The PFC can be subdivided in three major regions: orbital, medial, and lateral. Anatomy Background • Orbital and Medial emotional behavior. • Lateral cognitive support to the temporal organization of behavior, speech, and reasoning. Cognitive functions can only be understood in a broad connectionist context. Anatomy and connections • PFC is one of the latest cortices to develop, phylogenetically. • The PFC is connected with the brainstem and reciprocally the thalamus, the basal ganglia, and the limbic system. It is also connected with association cortices but not with primary cortices. • All PFC major regions are interconnected. • The memory networks of posterior cortex extend to PFC to shape the executive memory networks. Neuropsychology of the PFC • The three prefrontal “syndromes” – orbital PFC (eg. Ph.C) often induce dramatic changes of personality (disinhibition and disorder of attention). • inhibitory control to the hypothalamus, the basal ganglia and other neocortical areas – medial PFC lead to loss of spontaneity and difficulty in the initiation of movement • activated during sustained attention (PET, fMRI) – lateral PFC lead to inability to formulate and carry out plans and sequences of actions (and relative to language) • dysexecutive syndrome The PFC in the Cortical Cognitive Map The PFC in the Cortical Dynamics of Cognition • Role in the formation and recall of long-term memory – Left PFC encoding new memories – Right PFC retrieving stored memories • Routine, automatic, or overlearned behavioral sequences may be entirely organized in subcortical structures. • Action sequences with contingencies, ambiguities or uncertainties do engage the PFC. Two Forms of Temporal Sequencing of Actions PFC in the temporal organization of behavior • The major function of the lateral PFC is the temporal organization of behavior. – Served by • Attention • Working memory • Preparatory set. These three cognitive functions appear to work together in all the lateral areas of the PFC. PFC role in attention • Humans with lesions of anterior cingulate cortex (area 24) or the frontal eye fields (area 8) commonly exhibit some degree of spatial neglect and difficulties directing attention to discrete locations in visual space. • The orbital PFC plays a major role in the exclusionary aspect of attention. PFC involvement in attention (role in organizing goaldirected actions) orbitofrontal in the suppression of distractions lateral in the mediation of their cross-temporal contingencies Retrospective and prospective role of PFC • Working memory is the first temporal integrative function of the PFC to have been established electrophysiologically. – “Memory cells” retain visual, auditory or tactile memoranda that the animal must retain for subsequent motor response (memory for action). • Especially the lateral PFC is involved in the expectation of anticipated events (memory for the future). Coexistence in lateral PFC of two neural substrates of active representation, one for the recent past and the other for the anticipated future. Temporal Integration of Sound and Color in Frontal Cortex The integrative role of PFC is suggested against the “where-versus-what” specialization hypothesis. ---------Those networks associate, and thus encode, all the sensory and motor components of a task. Retrieval of an executive memory • Sensory inputs and internal environment activate a PFC network. • The network’s connectional architecture represents an action schema. • Then the sensory and motor processing are controlled by selective serial activations of the PFC in cooperation with subcortical structures and in continuous monitoring through feedback. Perception-Action cycle Conclusions • The PFC is one of the last territories of the neocortex to develop. • It is dedicated to the memory, planning, or execution of actions. • Orbital and medial PFC role in emotional behavior. • Lateral PFC cognitive functions for temporal organization of behavior. – Neuronal networks representing by associative connections the executive memory. Conclusions – To conduct its executive functions, the lateral PFC interacts with subcortical structures and with other parts of association cortex. – Temporal integration of information for the execution of prospective behavioral goals. • working memory and preparatory set. • All the integrative functions of the PFC operate within the context of the PerceptionAction Cycle that links the organism with its environment. P F C aw antaros oritsia Thank you!