Georg Stenberg

Motor imagery activates the cerebellum regionally. A SPECT rCBF study with 99mTc-HMPAO.

Our earlier findings of a cerebellar activation during motor imagery (Brain Res., 535 (1990) 313-317) were made with a technique with low regional resolution. Therefore we could not elucidate the distribution of the cerebellar activation. In the present study the cerebellar regional cerebral blood flow (rCBF) changes during motor imagery (MI) was measured with a single photon emission computed tomography (SPECT) rCBF method (99mTc-HMPAO) with higher regional resolution during (1) silent counting, and (2) MI (which included silent counting) in 17 normal subjects. Comparing the SPECT results from the two tasks revealed the regional activations during MI. We confirmed that the most pronounced regional activations during MI were found in the cerebellum, especially in its infero-lateral parts on both sides.

Judging Words at Face Value: Interference in a Word Processing Task Reveals Automatic Processing of Affective Facial Expressions

Earlier research has indicated that some characteristics of facial expressions may be automatically processed. This study investigated automaticity as evidenced by involuntary interference in a wor ...

Neurophysiological changes during insulin-induced hypoglycaemia and in the recovery period following glucose infusion in type 1 (insulin-dependent) diabetes mellitus and in normal man

SummaryHypoglycaemia (median venous blood glucose 1.8 mmol/l; range 1.6–2.3) was induced by an intravenous infusion of regular insulin in eight patients with Type 1 (insulin-dependent) diabetes mellitus (age 28.0±7.4 years; mean ± SD, duration 15.5±5.1 years) and in 12 age-matched healthy male control subjects. Multi-channel frequency analysis of electroencephalogram (electrophysiologic brain mapping) and recording of P300 and somatosensory evoked potentials were performed before, during and immediately after the hypoglycaemic period. The hypoglycaemia produced a significant increase in low frequency electroencephalographic activity in both groups, most pronounced over anterior regions of the brain. The electroencephalographic activity was normalised immediately after the hypoglycaemic period. The patients with diabetes showed somewhat longer P300 latencies during the initial normoglycaemic examination. Hypoglycaemia caused a marked reduction of the P300 amplitude in both groups of subjects and the amplitude was not restored immediately after normalisation of blood glucose levels. The somatosensory cortical responses were not affected by hypoglycaemia. We conclude that hypoglycaemia results in impairment in cerebral function, as measured by neurophysiological techniques, which is not immediately normalised when blood glucose is restored to normal.

Memory for perceived and imagined pictures: an event-related potential study

Event-related potentials (ERPs) and behavioural measures were used to investigate recognition memory and source-monitoring judgements about previously perceived and imagined pictures. At study, word labels of common objects were presented. Half of these were followed by a corresponding picture and the other half by an empty frame, signalling to the participants to mentally visualise an image. At test, participants in a source-monitoring task made a three-way discrimination between new words and words corresponding to previously perceived and imagined pictures. Participants in an old/new-recognition task indicated whether test words were previously presented or not. In both tasks, correctly identified old items elicited more positive-going ERPs than correctly judged new items. This widely distributed old/new effect was found to have an earlier onset and to be of a greater magnitude for imagined than for perceived items. Task (source versus item-memory) affected the old/new effects over prefrontal areas and the reaction times to remembered old items. The present findings are consistent with the view that a greater amount, or a different type, of information is necessary for accurate source-memory judgements than for correct recognition, and moreover, that different types of source-specifying information revive at different rates. In addition, the results add weight to the view that the late widespread ERP-old/new effect is sensitive to the quality or the amount of information retrieved from memory.

Conceptual and perceptual factors in the picture superiority effect

The picture superiority effect, i.e., better memory for pictures than for corresponding words, has been variously ascribed to a conceptual or a perceptual processing advantage. The present study aimed to disentangle perceptual and conceptual contributions. Pictures and words were tested for recognition in both their original formats and translated into participants’ second language. Multinomial Processing Tree (Batchelder & Riefer, 1999) and MINERVA (Hintzman, 1984) models were fitted to the data, and parameters corresponding to perceptual and conceptual recognition were estimated. Over three experiments, orienting tasks were varied, with neutral (Exp. 1), semantic (Exp. 2), and perceptual (Exp. 3) instructions, and the encoding manipulations were used to validate the parameters. Results indicate that there is picture superiority in both conceptual and perceptual memory, but conceptual processing makes a stronger contribution to the advantage of pictures over words in recognition.

Semantic processing without conscious identification: Evidence from event-related potentials

Three event-related potential (ERP) experiments examined whether semantic content can be accessed from visually presented words that cannot be consciously identified. Category labels were shown to participants, followed by masked, briefly exposed words that were either exemplars of the category or not exemplars. The task was to verify the category, by guessing if necessary, and to identify the word, naming it if possible. Exposure durations were selected to allow identification in approximately half the trials. For identified words, there was a marked difference in the ERP response between in-category and out-of-category words because of an N400 component. For unidentified words, there was a similar although smaller difference. Conscious identification was defined using a variety of approaches: verbal report, 6-alternative forced choice, and binary categorization (in the context of the regression method; A. G. Greenwald, M. R. Klinger, & E. S. Schuh, 1995). By any definition, ERPs for unidentified words showed evidence of semantic processing. In addition, there were differences in the neuronal populations recruited to process above-threshold versus below-threshold words, suggesting qualitative differences.

Personality and augmenting/reducing in visual and auditory evoked potentials

Previous studies have indicated a relationship between evoked potential augmenting/reducing and extraversion or sensation seeking. However, the proposed mechanism of protective inhibition can accou ...

Extraversion and the P300 in a visual classification task

Amplitude differences between extraverts and introverts in the P300 component of visual event-related potentials were examined in a picture classification task. A set of pictorial stimuli was used ...

Regional patterns of cortical blood flow distinguish extraverts from introverts

Summary-Eysenck’s hypothesis of higher cortical arousal in introverts was examined using regional cerebral blood flow measurement in 37 healthy subjects. The measurement was made at rest. using the “)Xe-inhalation method. Estimates of gray matter flow were obtained for 32 brain regions. There was no significant evidence of personality differences in general arousal, as measured by the mean flow level, averaged over all regions. There were. however, regional differences. An overall test of the blood flow distribution indicated different patterns of activity in introverts and extraverts. Follow-up tests attributed this to higher flow in the temporal lobes for introverts than for extraverts. Higher temporal lobe activity in introverts may be interpreted as increased functional connections between cortex and the limbic system. Related findings of personality alterations in temporal lobe epilepsy and the Kliiver-Bucy syndrome support this contention.

ATTENTION AND PERSONALITY IN AUGMENTING/ REDUCING OF VISUAL EVOKED POTENTIALS

Abstract Earlier research has shown that extraverts tend to increase their visual evoked potential amplitudes with increasing light intensity (augmenting), while introverts reach their maximum amplitude at lower intensities (reducing). The evoked response has normally been measured from association areas of the brain (at the vertex). The present study measured VEP amplitudes over visual cortex and at the vertex, using four light intensities in two conditions, where attention was either directed towards the light stimuli, or away from them by a concurrent auditory task. Forty subjects were classified as extraverts or introverts based on the Eysenck Personality Inventory. The results show that attention interacted significantly with extraversion. Introverts exhibited a narrower focus of attention, while higher amplitudes and amplitude-intensity functions when attending to the light flashes and lower when distracted. Extraverts showed smaller differences between conditions, indicating a more evenly distributed attention. Higher arousal in introverts is the probable cause of their narrower focus of attention. There were marked differences in the distribution of activity between vertex and occipital cortex. Introverts showed relatively stronger occipital responses and extraverts stronger vertex responses across all intensities and in both conditions. The predisposition for mainly perceptual responses to aversive stimuli in introverts, and for general alerting and motor preparatory responses in extraverts, are interpreted as supportive of Brebner and Coopers hypothesis that introverts are ‘geared to inspect’ and extraverts are ‘geared to respond’.