RESTING AND STIMULATED STATES IN FUNCTIONAL IMAGING STUDIES - EVIDENCE OF DIFFERENCES IN ATTENTIONAL AND INTENTIONAL SET

In a [Tc-99m]-hexamethylpropyleneamine oxime single photon emission co mputed tomography study of cerebral blood flow (CBF) in a visual activ ation paradigm (awake, eyes closed versus eyes open viewing a reversin g checkerboard pattern), the authors systematically measured previousl y observed qualitative alterations in frontal blood flow associated wi th visual stimulation (experiment 1). They confirmed a trend toward re ductions in CBF throughout precentral cortex that approached significa nce in areas 9 and 46, in conjunction with significant increases in CB F in postcentral cortices, Including visual association area PO, and a reas 3-12, 22, and 23. The authors posited that these changes may be r elated to differences in attentional and intentional state in the eyes -closed and eyes-open conditions. Such differences should be associate d with alterations in motor preparedness, leading to changes in respon se times and to alterations in thalamocortical gating of somatosensory information, which in turn lead to changes in somatosensory-evoked po tential amplitudes. In experiment 2, the authors measured simple motor response times to a 1500-Hz tone stimulus and early components of som atosensory-evoked potentials under the same experimental conditions. I n the visual stimulation condition, there was a significant increase L n the evoked potential amplitude (t = 2.686, p = 0.021), and a signifi cant decrease in response time (t = -2.464, p = 0.031). These observat ions provided tentative support for their hypothesis. The authors also demonstrated the major effect of normalization assumptions on regiona l blood flow measurements.