Academic journal article Cognitive, Affective and Behavioral Neuroscience

The Effects of Prefrontal Lesions on Working Memory Performance and Theory

Academic journal article Cognitive, Affective and Behavioral Neuroscience

The Effects of Prefrontal Lesions on Working Memory Performance and Theory

Article excerpt

The effects of experimental lesions of the monkey prefrontal cortex have played a predominant role in current conceptualizations of the functional organization of the lateral prefrontal cortex, especially with regard to working memory. The loss or sparing of certain performance abilities has been shown to be attributable to differences in the specific requirements of behavioral testing (e.g., spatial vs. non-spatial memoranda) along with differences in the specific locations of applied ablations (e.g., dorsal vs. ventral prefrontal cortex). Such findings, which have accumulated now for over a century, have led to widespread acceptance that the dorsolateral and ventrolateral aspects of the prefrontal cortex may perform different, specialized roles in higher order cognition. Nonetheless, it remains unclear and controversial how the lateral prefrontal cortex is functionally organized. Two main views propose different types of functional specialization of the dorsal and ventral prefrontal cortex. The first contends that the lateral prefrontal cortex is segregated according to the processing of spatial and nonspatial domains of information. The second contends that domain specialization is not the key to the organization of the prefrontal cortex, but that instead, the dorsal and ventral prefrontal cortices perform qualitatively different operations. This report critically reviews all relevant monkey lesion studies that have served as the foundation for current theories regarding the functional organization of the prefrontal cortex. Our goals are to evaluate how well the existing lesion data support each theory and to enumerate caveats that must be considered when interpreting the relevant literature.

The effects of experimental lesions of the monkey prefrontal cortex (PFC) have played a predominant role in current conceptualizations of prefrontal function, and most notably of working memory. Working memory allows organisms to use information that is not currently present in the environment but is vital to adaptive behavior. Current conceptualizations include both a maintenance component, akin to short-term memory, and an "executive" component that includes various control processes that in some way transform maintained representations into a more usable form. The loss or preservation of certain working memory abilities has been shown to be attributable to differences in the specific requirements of behavioral testing (e.g., spatial vs. nonspatial, delay vs. no delay) along with differences in the specific locations of applied ablations (e.g., dorsal vs. ventral PFC). Such findings, which have accumulated now for over a century, have led to widespread acceptance that the dorsolateral (BA 46, 9/46, and 9) and ventrolateral (BA 45 and 47/12) aspects of the PFC (see Figure 1) may perform different, specialized roles in higher order cognition.1 Nonetheless, it remains unclear and controversial how the lateral PFC is functionally organized.

Two main views propose different types of functional specialization for the dorsal and ventral PFC. The first, the material-specific model, contends that the lateral PFC is segregated according to the processing of spatial and nonspatial domains of information (Levy & Goldman-Rakic, 2000). The dorsolateral PFC is engaged in "on-line" maintenance of spatial memoranda, while the ventrolateral PFC supports nonspatial (e.g., face, objects) memoranda. In essence, the segregation of the dorsal "where" and ventral "what" visual pathways in posterior extrastriate, parietal, and temporal cortices are proposed to be conserved in the lateral PFC. This appealing hypothesis is founded on the relatively greater proportion of projections from the dorsal stream to the dorsolateral PFC and, similarly, the greater proportion of projections from the ventral stream to the ventrolateral PFC (see Figure 1). The second, process-specific model contends that domain specialization is not the key to the organization of the PFC. …

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