Evaluation of the Karolinska new positron camera system; the Scanditronix PC2048-15B

Proc. Natl. Acad. Sci. U.S.A.

1995

202

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 ...

Section: Methodsmentioning

confidence: 99%

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

Kawashima

O’Sullivan

Proc. Natl. Acad. Sci. U.S.A.

1995

202

“…The slice thickness was 5.0 mm for cross planes and 5.9 mm for direct planes in the center of field of view; or 6.0 mm for both 60 mm from the center of field of view [Litton et al, 1990;Evans et al, 19911. Each slice was independently reconstructed with a Hanning filter of 4 mm full width at halfmaximum (FWHM).…”

Section: Measurement Of Rcbfmentioning

confidence: 99%

Three‐dimensional analysis of clustered voxels in ¹⁵O‐butanol brain activation images

Levin

Kawashima

et al. 1993

Human Brain Mapping

118

104

Changes in the regional cerebral blood flow (rCBF) are often used as an indicator of changes in local neuronal activity of the brain. We present here quantitative measurements with positron emission tomography (PET) of rCBF with a freely diffusible flow tracer 150-butanol in control and activation states, and a pixel-by-pixel statistical parametric analysis of the rCBF changes combined with a cluster analysis. Anatomically standardized rCBF activation data from 39 normal subjects were analyzed for the occurrence of clustered voxels. Noise data was obtained from repeat measurements of rCBF with the brain in the activated state and from simulations. The variance in test-control images was largest outside the skull, and large in soft tissue regions around the brain. It was moderate but inhomogenous in gray matter, and low and homogenous in white matter. A special picture was generated of the conformation of sampled data with a normal distribution. In the gray and white matter, the pixel values were found to conform to a normal distribution, permitting calculation of Student's t-images. In the cluster analysis, activations are detected as clusters of voxels with high t-values. The clusters in activated regions, however, were considerably larger than the full width half-maximum of spatial autocorrelation function and were easily detected. Tables of the empirical Poisson-like distributions of the number of clusters of different sizes are provided, from which P values of the significance of the occurrence of clusters of different sizes can be estimated. o 1993 wiley-Liss, inc.

“…The head fixations in the NMR and PET scans were identical (23), so that the corresponding NMR and PET images would be superimposable. The PET scanning (15 transaxial slices at a distance of 6.5 mm) was made by a Scanditronix (Uppsala) PC2048-15B positron emission tomograph having a 4.5-mm in-plane spatial resolution (24,25). 1-[150]Butanol, a freely diffusible flow tracer, was used to measure regional cerebral blood flow (rCBF) (26).…”

Section: Methodsmentioning

confidence: 99%

Binocular disparity discrimination in human cerebralcortex: functional anatomy by positron emission tomography.

Gulyás

Proc. Natl. Acad. Sci. U.S.A.

1994

Neurobiological studies in higher primates indicate that the processing of stereoscopic information takes place at early levels in the visual cortex. To map the anatomical structures in the human brain participating in pure stereopsis based upon binocular disparity, we measured with positron emission tomography the changes in regional cerebral blood flow as an indicator of metabolic activity in 10 healthy young men during visual discrimination of binocular disparity. The data demonstrate that the discrimination of pure stereoptic disparity information takes place in the polar striate cortex and the neighboring peristriate cortices, as well as in the parietal lobe, the prefrontal cortex, and the cerebellum. The discrimination of stereoscopic depth is dependent on a network composed of multiple functional fields localized in occipital-and parietal-lobe visual areas as well as in the dorsolateral and mesial prefrontal cortex. The findings support the importance of coactivated occipitoparietal visual areas in the processing and analysis of binocular depth information in humans.Psychophysical studies in humans (1-3) have indicated that the various submodalities of visual perception may be processed and analyzed in the visual system by different "functional processing streams," which are, as in other higher primates (4-6), related to anatomically separable subdivisions ofthe visual pathways. Among others, stereopsis based on binocular disparity is a fundamental visual submodality (7)(8)(9)(10). Single-cell studies in the macaque monkey (11)(12)(13)(14) have revealed that many neurons in the striate cortex and in the peristriate cortices respond to binocular disparity stimulation. Nevertheless, the localization and extent of areas subserving stereoscopic vision at the levels of neuronal populations in primates, including humans, have not yet been revealed.Recently, positron emission tomography (PET) has been instrumental in demonstrating that, indeed, different modality-specific visual cortical areas in the human brain are involved in the early analysis of color, form, and motion information (15)(16)(17)(18)(19). By using PET with an experimental paradigm related to the detection of horizontal disparity, here we show those areas in the human brain which are specifically engaged in pure binocular disparity detection. METHODS Subjects. Ten healthy male volunteers [mean age; 32.6 + 11.9 (SD) years] participated in the present study. The subjects were fully informed about the objectives, details, and risks of the experiment, and they have given a written consent, in agreement with the Helsinki Declaration and the OPRR Reports (20). They denied any neurological, psychological, and ophthalmologic history. Eight of them were emmetropes, and two had corrected-to-zero vision. The study was approved by the Ethical, Radiation Safety, and Magnetic Resonance Committees ofthe Karolinska Hospital.Stimulus Design. The stimulus paradigms were designed with the following requirements in mind: Ci) in each task identical stimulus ...