Functional magnetic resonance imaging of human prefrontal cortex activation during a spatial working memory task.

Abstract

Hih-speed magnetic resonance (MR) imaging was used to detect activation in the human prefrontal cortex induced by a spatial working memory task modeled on those used to elucidate neuronal circuits in nonhuman primates. Subjects were required to judge whether the location occupied by the current stimulus had been occupied previously over a sequence of 14 or 15 stimuli presented in various locations. Control tasks were similar in all essential respects, except that the subject's task was to detect when one of the stimuli presented was colored red (color detection) or when a dot briefly appeared within the stimulus (dot detection). In all tasks, two to three target events occurred randomly. The MR signal increased in an area of the middle frontal gyrus corresponding to Brodmann's area 46 in all eight subjects performing the spatial working memory task. Right hemisphere activation was greater and more consistent than left. The MR signal change occurred within 6-9 sec of task onset and declined within a similar period after task completion. An increase in MR signal was also noted in the control tasks, but the magnitude of change was less than that recorded in the working memory task. These differences were replicated when testing was repeated in five of the original subjects. The localization of spatial working memory function in humans to a circumscribed area of the middle frontal gyrus supports the compartmentalization of working memory functions in the human prefrontal cortex and the localization ofspatial memory processes to comparable areas in humans and nonhuman primates.Working memory (1) provides temporary storage of information for cognitive capacities including comprehension and reasoning. The neural substrates for working memory have been elucidated in studies of nonhuman primates (2). Spatial working memory tasks requiring the brief storage of spatial information throughout the visual field engage neurons in the principal sulcus in the mid-dorsolateral cortex of rhesus monkeys (3, 4). Individual neurons in this region increase their discharge for particular target locations as monkeys recall the position of a previous stimulus (memory fields) (5). The same region is innervated by cortico-cortical projections from the posterior parietal cortex (6), where spatial perceptions are consolidated (7). These studies suggest that areas of the dorsolateral prefrontal cortex, by virtue of their extrinsic connections and physiological properties, are specialized for processing of spatial information in working memory.Positron emission tomography (PET) has recently been used to study working memory in humans. Petrides et al. (8) found that object working memory using pictures activated a region of the right middle frontal gyrus, including Brod-mann's area 9 and 46 and that these regions were activated bilaterally by a verbal working memory task (9). On the other hand, Paulescu et al. (10) found more posterior frontal activation in Broca's area (area 44) and parietal cortex (area 40) in a verbal working memor...

The role of prefrontal cortex in working-memory capacity, executive attention, and general fluid intelligence: An individual-differences perspective

“…Half of the subjects showed either bilateral dPFC activation during both tasks or matching unilateral dPFC activation in both tasks, consistent with the prior findings of similar lateralization in object and spatial tasks. However, the other half of the subjects showed bilateral activation in one of the tasks (most often the verbal task) and unilateral activation in the other, which was somewhat more consistent with the McCarthy group's f indings (McCarthy et al, 1994;McCarthy et al, 1996). We note, however, that no subjects showed uniquely right hemi-sphere activation in one task and uniquely left hemisphere activation in the other.…”

“…However, McCarthy and colleagues have found that dPFC activation varies between object and spatial WM tasks (McCarthy et al, 1994;McCarthy et al, 1996). 8 Here, when subjects monitored a stimulus stream for repetitions of objects, both hemispheres showed significant dPFC activation, with higher levels in the left hemisphere than in the right (but for the opposite result, see Callicott et al, 1999).…”

Exact and approximate judgements of visual and auditory numerosity: An fMRI study

“…These operations could be seen as emergent properties of the functional connections between parietal and frontal pre-motor and DLPF regions. Fronto-parietal functional loops are common to a wide range of cognitive operations where the active maintenance of information on line is necessary (Coull and Nobre, 1998;Jonides et al, 1998;Mccarthy et al, 1994). However, interestingly, the pattern of activation typically associated to generic mechanisms of temporal attention (i.e., attention to stimuli presented in different moment in time vs. in different spatial locations) tend to be left lateralised (Coull and Nobre, 1998), while attention to spatial positions or stimulus features is classically associated to bilateral activation (Corbetta and Shulman, 2002;Nobre, 2001;Wojciulik and Kanwisher, 1999).…”

Sensitivity of prefrontal cortex to changes in target probability: A functional MRI study

“…This association has been argued most extensively in the context of the P300, an event-related potential (ERP) elicited by infrequent events. Neuroimaging studies [Grasby et al, 1993;Jonides et al, 1993;Cohen et al, 1994;McCarthy et al, 1994;Casey et al, 1995;Smith et al, 1995;Kawashima et al, 1996;Casey et al, 1997] together with physiological studies in monkeys [Niki, 1974;Mishkin and Manning, 1978;Goldman-Rakic, 1987;Fuster, 1988;Yajeya and Fuster, 1988] have largely focused on the involvement of frontal regions in higher cognitive processes such as working memory and inhibitory control. These studies provide better spatial resolution than do electrophysiology studies and suggest that different regions within prefrontal cortex are associated with different types of processing.…”

“…These studies provide better spatial resolution than do electrophysiology studies and suggest that different regions within prefrontal cortex are associated with different types of processing. For example, dorsolateral prefrontal cortex has been implicated in working memory [Goldman-Rakic, 1987;Fuster, 1988;Cohen et al, 1994;McCarthy et al, 1994;Smith et al, 1995], while more ventral regions of prefrontal cortex have been implicated in the suppression of prepotent responses as in the go/no-go task [Kawashima et al, 1996;Casey et al, 1997;Konishi et al, 1999]. Few imaging studies have examined the effects of manipulating target probability on these presumed prefrontal functions.…”