Nerve cells in the monkey's prefrontal cortex and nucleus medialis dorsalis of the thalamus show changes of firing frequency associated with the performance of a delayed response test. Most cells increase firing during the cue presentation period or at the beginning of the ensuing delay; spike discharge highler than that in intertrial periods is present in some cells throughout the delay. These changes are interpreted as suggestive evidence of a role of frontothalamic circuits in the attentive process involved in short-term memory

No abstract

Anatomy and ConnectionsThe PFC is the association cortex of the frontal lobe. In Los Angeles, California 90095 primates, it comprises areas 8-13, 24, 32, 46, and 47 according to the cytoarchitectonic map of Brodmann The physiology of the cerebral cortex is organized in (1909), recently updated for the monkey by Petrides and hierarchical manner. At the bottom of the cortical organi-Pandya (Figure 1). Phylogenetically, it is one of the latest zation, sensory and motor areas support specific sencortices to develop, having attained maximum relative sory and motor functions. Progressively higher areas-of growth in the human brain (Brodmann, 1912; Jerison, later phylogenetic and ontogenetic development-support 1994), where it constitutes nearly one-third of the neocorfunctions that are progressively more integrative. The tex. Furthermore, the PFC undergoes late development in prefrontal cortex (PFC) constitutes the highest level of the course of ontogeny. In the human, by myelogenic and the cortical hierarchy dedicated to the representation synaptogenic criteria, the PFC is clearly late-maturing and execution of actions. cortex (Flechsig, 1920; Conel, 1939; Huttenlocher, 1990; The PFC can be subdivided in three major regions: Huttenlocher and Dabholkar, 1997). In the monkey's orbital, medial, and lateral. The orbital and medial re-PFC, myelogenesis also seems to develop late (Gibson, gions are involved in emotional behavior. The lateral 1991). However, the assumption that the synaptic strucregion, which is maximally developed in the human, proture of the PFC lags behind that of other neocortical vides the cognitive support to the temporal organization areas has been challenged with morphometric data of behavior, speech, and reasoning. This function of (Bourgeois et al., 1994). In any case, imaging studies temporal organization is served by several subordinate indicate that, in the human, prefrontal areas do not attain functions that are closely intertwined (e.g., temporal infull maturity until adolescence (Chugani et al., 1987; tegration, working memory, set). Whatever areal special-Paus et al., 1999; Sowell et al. , 1999). This conclusion ization can be discerned in the PFC is not so much is consistent with the behavioral evidence that these attributable to the topographical distribution of those areas are critical for those higher cognitive functions functions as to the nature of the cognitive information that develop late, such as propositional speech and with which they operate. Much of the prevalent confureasoning. sion in the PFC literature derives from two commonThe profuse variety of connections of the PFC is obvierrors. The first is to argue for one particular prefrontal function while opposing or neglecting others that complement it; the second is to localize any of them within a discrete portion of PFC.The functions of the PFC rely closely on its connections with a vast array of other cerebral structures. None of its cognitive functions can be understood if taken out of a broad connectionist context. Any hyp...

No abstract