Positron-emission tomography studies of cross-modality inhibition in selective attentional tasks: closing the "mind's eye".

Abstract

It is a familiar experience that we tend to close our eyes or divert our gaze when concentrating attention on cognitively demanding tasks. We report on the brain activity correlates of directing attention away from potentially competing visual processing and toward processing in another sensory modality. Results are reported from a series of positron-emission tomography studies of the human brain engaged in somatosensory tasks, in both "eyes open" and "eyes closed" conditions. During these tasks, there was a significant decrease in the regional cerebral blood flow in the visual cortex, which occurred irrespective ofwhether subjects had to close their eyes or were instructed to keep their eyes open. These task-related deactivations of the association areas belonging to the nonrelevant sensory modality were interpreted as being due to decreased metabolic activity. Previous research has clearly demonstrated selective activation of cortical regions involved in attention-demanding modalityspecific tasks; however, the other side of this story appears to be one of selective deactivation of unattended areas.Regional cerebral blood flow (rCBF) changes in the human brain have now been extensively studied by positron-emission tomography (PET) methods (1). Regional changes in rCBF are monotonically related to regional changes in cerebral metabolic rate, in particular the metabolic demands of maintaining the transmembrane ionic gradients of active neurons (1-4). Brain structures that actively participate in the performance of specific cognitive tasks can be identified as discrete regions of increase in rCBF. During specific cognitive tasks, our attention is selectively focused on the relevant sensory modality or submodality from which information is necessary to successfully perform the task. In behavioral terms, stimuli within the focus of attention are generally discriminated more quickly and accurately, are registered more vividly in awareness and memory, and exert greater control over behavior than do unattended stimuli (5, 6). In physiological terms, selective attention is described as changes in the excitability of cortical neurons that are limited to, or focused on, a specific sensory modality or submodality (1, 7). Increases in rCBF associated with these changes in synaptic metabolic activity can then be identified in modality-specific tasks (8, 9). Behavioral models of selective attention generally accept the notion that attention has a limited capacity, which must be flexibly distributed among competing processes (5). The question arises, therefore, what is happening neurobiologically to cortical areas of another sensory modality which is not being attended during the performance of a task? In particular, is there evidence of inhibition or deactivation in these regions which are not being attended during the performance of a cognitive task?To answer this question, we performed two PET studies in nine normal volunteers while they were engaged in somatosensory tasks [roughness discrimination (10) and tactile ...

Faces evoke spatially differentiated patterns of BOLD activation and deactivation

“…Prior studies have demonstrated effects of this kind. Using positron emission tomography (PET) to measure changes in regional cerebral blood flow (rCBF) during somatosensory and visual tasks, Kwashima et al [15] observed task-related deactivations in sensory areas involved in processing information directed to the irrelevant or unattended sensory modality. Similarly, in an fMRI study by Laurienti et al [16], auditory stimuli elicited activation in auditory cortex and deactivation in extrastriate visual cortex and vice versa.…”

“…Task-related decreases in BOLD contrast (deactivations) have been reported in fMRI studies [14][15][16][17] and have been correlated with decreased blood oxygenation and neural suppression [17]. Functional neuroimaging studies could therefore provide the desired converging evidence by determining whether a stimulus category, such as faces, evokes spatially discrete BOLD contrast activations and deactivations.…”

Common deactivation patterns during working memory and visual attention tasks: An intra‐subject fMRI study at 4 Tesla

“…Positron emission tomography (PET) also showed rCBF-decreases in visual (Kawashima, et al 1995) and auditory (Shulman, et al 1997) cortices during spatial-, visual-or selectiveattention tasks, and in auditory and somatosensory cortices during tasks that did not require attention. (Born, et al 2002;Haxby, et al 1994;Shulman, et al 1997) Brain deactivation also has been reported during attention requiring tasks (Deary, et al 2004;Hester, et al 2004;Lawrence, et al 2003); however, whether it reflects neural inhibition of task-irrelevant neural processing or hemodynamic compensatory mechanisms in the brain is still unclear.…”

Changing channels: An fMRI study of aging and cross-modal attention shifts

“…Studies of young adults suggest, however, that the principles of selective processing are similar in other sensory modalities and when shifting attention across sensory modalities (Kawashima et al 1995;Woodruff et al 1996). To investigate whether age-related processing inefficiencies observed in visual attention are similar in auditory attention and when shifting attention across modalities, we conducted an FMRI study with healthy younger and older adults.…”