Frank Uhl

Cerebral correlates of imagining colours, faces and a map—I. SPECT of regional cerebral blood flow

The distribution of regional cerebral blood flow (rCBF) was assessed by single photon emission computerized tomography (SPECT) in subjects during a resting state and during imagining either colours or faces or a route on a map. Twelve out of 30 subjects reported the spontaneous occurrence of mental visual images during the resting state. In these subjects flow in both orbitofrontal regions was higher than in those subjects who had not experienced spontaneous imagery. Voluntary imagery led to an increase of regional flow indices in basal temporal regions of both hemispheres and to a rightwards shift of global hemispheric asymmetry. The local changes were distinctly more marked with faces than with any of the other two stimuli. Imagining faces was also the only condition that led to an increase of activity in the left inferior occipital region which has been suggested by previous studies as being a crucial area for visual imagery. It is concluded that the observed differences of rCBF patterns between imagery conditions are related to the amount of information conveyed by the mental image. In contrast to the results of a companion study on DC-shifts accompanying imagery there was no effect of the visual versus spatial character of the images.

Tactile mental imagery in sighted persons and in patients suffering from peripheral blindness early in life

Patterns of cortical activity as measured by scalp-recorded event-related slow negative DC potential shifts were recorded in 9 early blind and 23 sighted normals while they imagined the feel of textures with the fingertips of one hand. All sighted subjects reported to have concomitant visual imagery as well. Hence, it was not surprising to observe occipital negative shifts, previously described as a sign of occipital visual cortex involvement in visual mental imagery. Though having never had visual perception, the blind, too, had occipital negativities. Their absolute amplitudes were smaller than in the sighted, not only occipitally but also and more pronounced at other areas, particularly frontally where amplitudes were even positive. On the hypothesis that the smaller overall amplitudes in the blind could obscure topographical differences between groups, the relative distribution of negativity across the scalp was assessed, using normalized data. Such normalized parameters significantly differed between groups, indicating that the occipital potentials of the blind were relatively more negative as related to the other scalp areas, than were the occipital potentials of the sighted as related to the other scalp areas. This occipital finding might indicate a participation of the blinds visually deprived occipital cortex in tactile imagery. Second, parietal DC potentials were maximal over the hemisphere contralateral to the imaging hand, possibly indicating involvement of the contralateral parietal association cortex in tactile imagery. Reasons why this was true only for the sighted, are discussed.

Anterior frontal cortex and the effect of proactive interference in word pair learning —results of brain-spect

Technetium-99m-HMPAO-Brain-SPECT was performed twice in each of 12 right-handed students. The control condition was a standard word pair learning task. In the experimental condition, subjects had to overcome the detrimental effect that older memories exerted on the acquisition of new information (controlling proactive inhibition): they were presented with taxonomically similar words, which could easily be mixed up, and which reappeared in each list, but in different pairings. Results revealed an increase in right anterior frontal flow indices with the experimental condition. These results parallel the observed increase in negative event-related DC potential shifts. UHL et al. [J. cognit. Neurosci. 2, 373, 1990] recorded at frontopolar (Fp3, Fp4) scalp projections, although the extent of modulation was much higher for DC potentials (100%) than it was for SPECT (3%) thus suggesting different sensitivity.

Elaborative strategies in word pair learning―DC-potential correlates of differential frontal and temporal lobe involvement

Cortical DC potentials were recorded while subjects were learning word pairs. The use of an elaborative mnemonic strategy resulted in a left frontal sustained negative shift. Its amplitude was independent of whether imagery mnemonics or semantic mnemonics were used. By contrast, posterior temporal potentials differed according to strategy: with imagery mnemonics, subjects had more symmetrical potentials over posterior temporal areas whereas with a semantic strategy, there was a left hemispheric preponderance of the DC potential. An interpretation within Stuss and Bensons theory on the frontal lobes is given.

Unimanual motor learning impaired by frontomedial and insular lesions in man

We correlated impaired unimanual motor learning with the lesion site in 53 patients with chronic lesions predominantly of the frontal lobe. The lesions were assessed using computed tomography (CT), then transferred to standard templates of nine slices parallel to the canthomeatal plane and digitized with a raster matrix of 3 mm by 3 mm width. The learning task was to track a moving target on a computer screen with a dot guided by the preferred hand, while the horizontal coupling between hand movement and screen was inverted. The mean tracking error was recorded over eight successive trials of 80s duration. If the mean error of the last three trials was not lower than that of the first three trials, impaired motor learning was assumed. We correlated performance and lesion with a contingency table analysis for each raster element. Impaired motor learning was associated with a lesion within the supplementary motor area and adjacent anterior cingulate, and within the anterior insular region. Our results indicate that these regions are critical for motor learning and functional plasticity in man. Our data support activation patterns obtained with positron emission tomography.

Frontomesial Activation during Spatial Bilateral Coordination: Tentative Conclusions on SMA Function

Lang et al. (1988) established that increased demands on the timing and sequencing of complex movements resulted in increased DC shifts at the anterior midline. This finding was interpreted in favor of a predominant role of frontomesial structures, including the SMA, for temporal as opposed to spatial properties of a movement. The present study investigated whether frontomesial activity is totally independent of spatial properties of a movement. Two bilateral movements differing by the direction of rotation were compared. Continuous, smooth rotation movements (see Figure 23-1) were chosen in order to minimize sequencing or reinitiation.