Universal positive correlations between different cognitive tests motivate the concept of “general intelligence” or Spearman's g . Here the neural basis for g is investigated by means of positron emission tomography. Spatial, verbal, and perceptuo-motor tasks with high- g involvement are compared with matched low- g control tasks. In contrast to the common view that g reflects a broad sample of major cognitive functions, high- g tasks do not show diffuse recruitment of multiple brain regions. Instead they are associated with selective recruitment of lateral frontal cortex in one or both hemispheres. Despite very different task content in the three high- g –low- g contrasts, lateral frontal recruitment is markedly similar in each case. Many previous experiments have shown these same frontal regions to be recruited by a broad range of different cognitive demands. The results suggest that “general intelligence” derives from a specific frontal system important in the control of diverse forms of behavior.
and in reverse (Owen et al., 2000) or alphabetical (Postle et Brain Sciences Unit al., 1999) order prior to making a response. Evidently, 15 Chaucer Road in such cases the task is substantially harder when reor-Cambridge CB2 2EF ganization is required. This confound is important be-United Kingdom cause increasing task difficulty is itself associated with 2 Department of Psychology DLPFC activation in many different cognitive domains University of Hertfordshire (Duncan and Owen, 2000). Hatfield In the present study we sought direct evidence for a United Kingdom role of prefrontal cortex in a well-defined working mem-3 Wolfson Brain Imaging Centre ory strategy. In the working memory literature, the best-University of Cambridge studied strategy is perhaps performance improvement Cambridge through chunking. An opportunity to reorganize materi-United Kingdom als into familiar or regular structures can increase working memory capacity, sometimes very substantially (Ericcson et al., 1980). In domains from sending and Summary receiving Morse code (Bryan and Harter, 1899) to chess (Chase and Simon, 1973), chunking has been proposed It is often proposed that prefrontal cortex is importantas the major basis for increasing expertise through in organization and control of working memory conlearning. We investigated chunking in a standard spatial tents. In some cases, effective reorganization can deworking memory task by manipulating the extent to crease task difficulty, implying a dissociation between which sequences of stimuli could be encoded into memfrontal activity and basic memory demand. In a spatial ory as simple configural representations. We predicted working memory task, we studied the improvement of that trials that allowed such chunking would be less performance that occurs when materials can be reordifficult to remember than trials that did not allow chunkganized into higher level groups or chunks. Structured ing. Despite this decrease in task difficulty, we predicted sequences, encouraging reorganization and chunking, increased recruitment of the lateral prefrontal cortex. were compared with unstructured sequences. ThoughIn an initial, large-scale behavioral study, we acquired structured sequences were easier to remember, eventdirect evidence that reorganization of structured serelated functional magnetic resonance imaging (fMRI) quences into higher level chunks is an effective strategy showed increased activation of lateral frontal cortex, in spatial working memory. In a second study, we used in particular during memory encoding. The results event-related functional magnetic resonance imaging show that, even when memory demand decreases, (fMRI) to compare brain activity during structured and organization of working memory contents into higher unstructured sequences. A control fMRI study shows level chunks is associated with increased prefrontal that the difference between structured and unstructured activity.sequences is specifically associated with their role in the working memory task.
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