Soc. Neurosci. Abstr. 1999.10

BRAIN REGIONS INVOLVED IN MAINTENANCE OF ATTENTION AND SHIFTING BETWEEN GLOBAL AND LOCAL STRUCTURES OF VISUAL PATTERNS: A PET STUDY IN MACAQUE MONKEYS H.-K.

Tanaka1*, H. Onoe3, 4 , H. Tsukada5 and I. Fujita1, 2, 3. 1Dept. Cogni. Neurosci., Med. Sch. and 2Grad. Sch. Eng. Sci., Osaka Univ., 3CREST, JST, Osaka, 4Dept. Psychol., Tokyo Metropol. Inst. Neurosci., Tokyo, 5Central Res. Lab., Hamamatsu Photonics, Shizuoka, Japan.

To identify brain areas involved in maintenance of visual attention and shifting between global and local structures of stimulus patterns, we applied positron emission tomography (PET) techniques to measure the regional cerebral blood flow (rCBF) in monkeys during a visual discrimination task. Visual stimuli were large letters (N, Z, reversed N, or reversed Z; 2.7x2.7 deg2) made of a string of the same small letters (N, Z, reversed N, or reversed Z; 0.4x0.4 deg2) (e.g., a large N made of 13 small reversed Ns). Two monkeys (Macaca fuscata) were trained to detect a target (N or Z) which appeared pseudorandomly at either the global or the local level of the visual stimulus ("global or local trials"). The monkeys were supposed to shift their attention between the global and local levels of the stimulus patterns when a sequence of trials changed between global and local trials. The number of switches between global and local trials was varied from 1 to 9 in the first 24-sec epoch of each scan, while the number of global trials were kept the same as that of local trials throughout all PET scans. We identified brain areas whose rCBF changed with the number of target switches using the SPM 95 software. An increase in the rCBF in the posterior part of the lateral intraparietal (LIP) area was positively correlated with the number of target switches between the two levels. On the other hand, an increase in the rCBF in the medial frontal cortex including Brodmann's areas 14, 24, 25 and 32, was negatively correlated with the number of target switches. The two areas were the only areas whose rCBF was significantly correlated with the number of switches in a consistent manner in the two monkeys. The results suggest that area LIP is involved in the shifting of attention between global and local levels of visual patterns, whereas the medial frontal areas are involved in the maintenance of attention at one level. (supported by CREST)

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