Isolating the mnemonic component in spatial delayed response: A controlled PET ¹⁵O-labeled water regional cerebral blood flow study in normal humans

In this study we attempted to elucidate the neural network involved in maintaining spatial information over short delays by means of the PET ¹⁵O-labeled water method for measuring regional cerebral blood flow. To isolate the mnemonic component of delayed response processing we designed a control task isomorphic to the experimental task (in which the subject remembered the location of four targets in an array over a 7 s delay) and controlled for spatial encoding. Fourteen normal subjects participated in the study. Regional cerebral blood flow (rCBF) data were analyzed using statistical parametric mapping, a data-driven approach which canvasses the whole brain for significantly activated pixels in the experimental visà-vis the control task, and a hypothesis driven region of interest approach involving comparisons of control and experimental conditions using normalized rCBF data. We found convergent evidence for a spatially distinct but functionally related network in which dorsolateral prefrontal cortex and extrastriate occipital cortex were activated by the experimental task visà-vis the control task, as well as evidence for superior parietal and supplementary motor area cortical activation. These findings suggest that anterior components of the network may be involved in mnemonic rehearsal functions, while posterior components may store critical perceptual attributes of the memoranda.