Neural mechanisms underlying spatial judgements on seen and imagined visual stimuli in the left and right hemifields in men.

Full Abstract

We investigated the neural networks involved in spatial judgements on visual and imagined stimuli in the left and right hemifields. Twenty healthy male right-handers were scanned using fMRI. In an adaptation of the Mental Clock Test, subjects judged whether the angle between visually presented or to be imagined clock hands at a given time (e.g. "12:20") was >90 degrees or <90 degrees . The angle formed by the clock hands was always located either on the left or right hemifield of the clock face, constituting a 2x2 factorial design with factors stimulus type (visual "V", imagined "I") and attention to spatial hemifield (left "L", right "R"). The contrast I>V revealed a bilateral neural network which included the superior parietal, prefrontal and antero-dorsal cingulate cortex. While right superior parietal cortex was activated during both RV and LV, left superior parietal cortex was only active during RV. The contrast RI versus LI (and vice versa) did not reveal significant differences with respect to activation height. However, a masking procedure and the calculation of a laterality index showed that RI recruited larger areas in the left than in the right hemisphere, while LI led to symmetrical activations in both hemispheres. Our data thus confirm that there are hemifield-specific asymmetries in brain activity during spatial processing of both visual and imagined stimuli. Our data indicate, however, that these asymmetries are less clear and of a different nature in the latter. Overall, our findings converge with neuropsychological data showing that representational and visuospatial neglect do not always co-occur.

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Author information

Author/s: Kukolja, Juraj (J); Marshall, John C (JC); Fink, Gereon R (GR);

Affiliation: Institute of Medicine, Cognitive Neurology Group, Research Centre Jülich, Germany. j.kukolja(-atsign-)fz-juelich.de

Journal and publication information

Publication Type: Comparative Study; Journal Article; Research Support, Non-U.S. Gov't

Journal: Neuropsychologia (Neuropsychologia), published in England. (Language: eng)

Reference: 2006-; vol 44 (issue 14) : pp 2846-60

Dates: Created 2006/10/18; Completed 2006/12/12;

PMID: 16934843, status: MEDLINE (last retrieval date: 12/26/2008)

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MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Adult
Brain Mapping
Eye Movements - physiology
Functional Laterality - physiology
Humans
Imagination - physiology
Judgment - physiology

Judgment - physiology
Male
Photic Stimulation - methods
Reaction Time - physiology
Space Perception - physiology
Time Factors
Visual Cortex - physiology

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