Biomedical subjects

J Krasuski

Publications and source records attributed to J Krasuski.

4 recordsLinked to original sources

PubMed2001

Muscarinic versus nicotinic modulation of a visual task. a pet study using drug probes.

Little is known about acetylcholine (ACh) modulation of central visual processing in humans. Receptor densities in visual brain regions are differentially distributed suggesting that receptor subtypes have different functions. Using PET, we have previously described the brain regions activated by a simple pattern-flash stimulus in healthy elderly subjects. To evaluate muscarinic and nicotinic contributions to ACh modulation of visual processing, we scanned elderly subjects watching the pattern-flash stimulus during no drug, during physostigmine augmentation, and during scopolamine antagonism of physostigmine's action. These manipulations of ACh significantly altered regional cerebral blood flow (rCBF) in brain regions activated by the task. The pattern of rCBF values across drug conditions suggested that muscarinic and nicotinic effects were dissociated. Muscarinic action predominated in striate cortex (Brodmann Area, BA 17) and lateral visual association areas (BA 18, 19), while nicotinic action predominated in the thalamus and inferior parietal regions (BA 39/40). Both muscarinic and nicotinic actions increased rCBF in some regions while decreasing it in others. A parsimonious reconciliation of these results with functional anatomy suggests that muscarinic action modulates visual attribute processing, while nicotinic action modulates arousal and selective attention to the visual task.

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PubMed1998

Increasing required neural response to expose abnormal brain function in mild versus moderate or severe Alzheimer's disease: PET study using parametric visual stimulation.

OBJECTIVE: The authors examined the interaction of Alzheimer's disease severity and visual stimulus complexity in relation to regional brain function. METHOD: Each subject had five positron emission tomography [15]H2O scans while wearing goggles containing a grid of red lights embedded into each lens. Regional cerebral blood flow (CBF) was measured at 0 Hz and while lights were flashed alternately into the two eyes at 1, 4, 7, and 14 Hz. Changes in regional CBF from the 0-Hz baseline were measured at each frequency in 19 healthy subjects (mean age = 65 years, SD = 11), 10 patients with mild Alzheimer's disease (mean age = 69, SD = 5; Mini-Mental State score > or = 20), and 11 patients with moderate to severe Alzheimer's disease (mean age = 73, SD = 12; Mini-Mental State score < or = 19). RESULTS: As pattern-flash frequency increased, CBF responses in the comparison group included biphasic rising then falling in the striate cortex, linear increase in visual association areas, linear decrease in many anterior areas, and a peak at 1 Hz in V5/MT. Despite equivalent resting CBF and CBF responses to low frequencies among all groups, the groups with Alzheimer's disease had significantly smaller CBF responses than the comparison group at the frequency producing the largest response in the comparison group in many brain regions. Also, patients with moderate/severe dementia had smaller responses at frequencies producing intermediate responses in comparison subjects. CONCLUSIONS: Functional failure was demonstrated in patients with mild dementia when large neural responses were required and in patients with moderate/severe dementia when large and intermediate responses were required.

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PubMed1997

Attention-related modulation of activity in primary and secondary auditory cortex.

We investigated the effects of auditory attention on brain activity using functional magnetic resonance imaging. Subjects listened to three word lists, three times each, and were instructed to count the number of times they heard a target word during two of these presentations. For the third, they listened to the words without counting. All subjects showed significant areas of activation in auditory cortex during the listening conditions compared to rest. There was significantly more activation and a larger area of activation, particularly in association cortex, in the left temporal lobe during counting of targets compared to the no-target conditions, with a similar trend in the right hemisphere. These results provide evidence of an attention-related enhancement of both activation magnitude and extent in auditory cortex.

Adult↗

PubMed1997

Frequency variation of a pattern-flash visual stimulus during PET differentially activates brain from striate through frontal cortex.

We evaluate regional cerebral blood flow (rCBF) in 19 healthy elderly subjects, mean age 64 +/- 11 (SD, years), during a passive visual stimulus in which pattern-flash frequency was parametrically manipulated. Using goggles with a grid of red lights imbedded into each lens, we performed five positron emission tomography (PET) H2(15)O water scans on each subject at alternating (left to right eye) flash frequencies of 0, 1, 4, 7, and 14 Hz. We found a biphasic rising and falling rCBF response in the striate cortex (7 Hz peak) and left anterior cingulate (4 Hz peak), 1 Hz activation in left middle temporal gyrus (V5), monotonically increasing rCBF in posterior areas (lateral and inferior visual association areas, Brodmann 18 and 19), and monotonically decreasing rCBF in anterior areas (frontal, cingulate, and superior temporal) predominantly in right hemisphere. We suggest the striate rCBF changes at all frequencies primarily reflect lateral geniculate input, the middle temporal activation at 1 Hz reflects perception of apparent motion, and the posterior extrastriate rCBF monotonic increase represents a neural response to increasing luminance intensity and form and color complexity that occur as pattern-flash frequency increases. The anterior monotonic rCBF decrease may represent active cross-modal functional suppression of brain areas irrelevant for processing the passive visual stimulus. Pattern-flash rCBF responses were highly reproducible (no series effect), more so in posterior than in anterior brain regions. The reproducibility and systematically changing rCBF responses to this passive stimulus suggest that it could be successfully used as a disease probe to evaluate neural function and drug effects in cognitively impaired patients.

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