Biomedical subjects

Rolf Verleger

Publications and source records attributed to Rolf Verleger.

11 recordsLinked to original sources

PubMed2004

Sleep inspires insight.

Insight denotes a mental restructuring that leads to a sudden gain of explicit knowledge allowing qualitatively changed behaviour. Anecdotal reports on scientific discovery suggest that pivotal insights can be gained through sleep. Sleep consolidates recent memories and, concomitantly, could allow insight by changing their representational structure. Here we show a facilitating role of sleep in a process of insight. Subjects performed a cognitive task requiring the learning of stimulus-response sequences, in which they improved gradually by increasing response speed across task blocks. However, they could also improve abruptly after gaining insight into a hidden abstract rule underlying all sequences. Initial training establishing a task representation was followed by 8 h of nocturnal sleep, nocturnal wakefulness, or daytime wakefulness. At subsequent retesting, more than twice as many subjects gained insight into the hidden rule after sleep as after wakefulness, regardless of time of day. Sleep did not enhance insight in the absence of initial training. A characteristic antecedent of sleep-related insight was revealed in a slowing of reaction times across sleep. We conclude that sleep, by restructuring new memory representations, facilitates extraction of explicit knowledge and insightful behaviour.

Adolescent↗

PubMed2004

Being prepared on time: on the importance of the previous foreperiod to current preparation, as reflected in speed, force and preparation-related brain potentials.

How do participants adapt to temporal variation of preparatory foreperiods? For reaction times, specific sequential effects have been observed. Responses become slower when the foreperiod is shorter on the current than on the previous trial. If this effect is due to changes in motor activation, it should also be visible in force of responses and in EEG measures of motor preparation, the contingent negative variation (CNV) and the lateralized readiness potential (LRP). These hypotheses were tested in a two-choice reaction task, with targets occurring 500, 1500, or 2500 ms after an acoustic warning signal. The reaction time results showed the expected pattern and were accompanied by similar effects on a fronto-central CNV and the LRP. In contrast, the increase of response force with brief current foreperiods did not depend on previous foreperiods. Thus, EEG measures confirm that sequential effects on RT are at least partially due to changes in motor activation originating from previous trials. Effects found on response force may be related to general response readiness rather than activation of motor-hand areas, which may explain the absence of a sequential effect on force in the current experiment.

Adult↗

PubMed2004

On the role of the cerebellum in exploiting temporal contingencies:; evidence from response times and preparatory EEG potentials in patients with cerebellar atrophy.

Patients with degenerative cerebellar disease were compared to healthy controls in their ability to adapt behaviour to temporal contingencies, both according to instructions and according to acquired experience. Participants had to press the cued key whenever the inside of a clock face changed its colour, which could occur when the pointer, rotating once every 4s, was at "10h" or at "12h" or at "2h". Probabilities varied between blocks at which of these three time points the colour change occurred, with participants being instructed accordingly. Response times correlated intraindividually with these instructed "a priori" probabilities in control participants only. Subjectively, at any moment, probabilities of occurrence depend on whether the imperative colour change had occurred before, thus may be better described by conditional ("a posteriori") probabilities. Indeed, when response times were correlated to a posteriori rather than a priori probabilities, correlations increased in both groups equally from their different a priori levels. The amplitudes of preparatory EEG negativity before responding tended to obey to the same relationships, suggesting that the difference between groups was not due to pure motor impairment. Thus, these data suggest that patients with cerebellar atrophy are more impaired in implementing and using task-relevant information in a top-down manner than in learning to modify task-relevant contingencies.

Adult↗

PubMed2003

How the self controls its "automatic pilot" when processing subliminal information.

Human performance may be primed by information not consciously available. Can such priming become so overwhelming that observers cannot help but act accordingly? In the present study, well-visible stimuli were preceded by whole series of unidentifiable stimuli. These series had strong, additive priming effects on behavior. However, their effect depended on the frequency with which they provided information conflicting to the visible main stimuli. Thus, effects of subliminal priming are under observers' strategic control, with the criterion presumably set as a function of the openly observable error frequency. Electrical brain potentials show that this criterion acts simultaneously at the level of visual discrimination of the primes and at motor activation evoked by the primes, thereby shielding observers from unwanted information.

Consciousness↗

PubMed2003

Signs of REM sleep dependent enhancement of implicit face memory: a repetition priming study.

Faces are processed and stored in distinct neuroanatomical systems. Based on evidence of a critical role of sleep in memory processes, we investigated the impact of nocturnal sleep on implicit memories for faces in healthy men. Face repetition effects in reaction times were compared across sleep periods early in the night, which are dominated by slow wave sleep (SWS), and late in the night, where rapid eye movement (REM) sleep prevails, as well as across corresponding nocturnal intervals of wakefulness. An inverse priming effect was found selectively across REM sleep rich late sleep, as indicated by distinctly prolonged response latencies to previously presented faces compared with novel faces after this period of sleep (P<0.05). We assumed this inverse priming to reflect a facilitated identification of previously presented faces after extended REM sleep periods, thereby producing interference with the response generation in our task which did not require face identification but rather required recognizing formal features of the faces. This interpretation was supported by a supplementary experiment where enhanced positive repetition priming was found across late, REM sleep dominated sleep in a task requiring face identification. Together, these findings indicate that implicit face memories particularly benefit from REM sleep associated brain mechanisms.

Circadian Rhythm↗

PubMed2003

Effects of same- and different-modality cues in a Posner task: extinction-type, spatial, and non-spatial deficits after right-hemispheric stroke.

The response delay to left target stimuli preceded by right-side cues, first described by Posner et al. [J. Neurosci. 4 (1984) 1863-1874] appears to be a stable marker of right-parietal injury. However, only few studies compared patients' performance to age-matched controls. Furthermore, only few studies compared visual and auditory stimuli in this task. Therefore, two groups of right-hemisphere stroke patients, with and without left visual hemineglect, and a healthy control group were studied in three versions of Posner's paradigm. Visual or auditory target stimuli were presented to the subject's left or right, following a visual or auditory cue by 150 ms. The classical 'extinction-type' effect, an increase in missing responses for right visual cue/left visual target, was specifically observed in neglect patients. In the same condition, an 'extinction-type' response delay was present in patients with neglect and in those without neglect. No such delay occurred in any group when cues were auditory. Specifically in neglect patients, response times were generally longer for left than for right visual targets, regardless of cue side and of cue modality. Response times were generally prolonged in neglect patients regardless of target modality. This suggests that three components impair neglect patients' performance in this paradigm: a non-spatial, supramodal deficit, a global, neglect-type deficit of the contralesional hemi-field, and the extinction-type impairment. The latter two deficits appear to be most marked within the visual domain.

Acoustic Stimulation↗

PubMed2003

Control of hand movements after striatocapsular stroke: high-resolution temporal analysis of the function of ipsilateral activation.

OBJECTIVE: Hemiparesis due to infarction of the middle cerebral artery has become an increasingly important focus of research on cortical plasticity. Positron emission tomography and functional magnetic resonance imaging studies in such patients found involvement of the hemisphere ipsilateral to the affected hand related to movements of this hand. To understand the function of this ipsilateral activation, the present study investigated movement-related electroencephalogram (EEG) potentials in patients and healthy control subjects to measure timing of ipsi- and contralateral activation relative to movement onset. METHODS: Thirteen patients were investigated in their chronic stage. Their pyramidal tracts were affected by infarctions of the middle cerebral artery at striatocapsular level. EEG potentials were recorded from 26 scalp electrodes while patients were pressing a key with their right or left index finger within a warned choice-response task. RESULTS: Beginning 200 ms before responses of the affected hand, there was normal contralateral preponderance of EEG negativity. Briefly after response onset, however, the other unaffected hemisphere, ipsilateral to the responding hand, became additionally active. This pattern did not occur with responses made by the unaffected hand nor in healthy participants. CONCLUSIONS: The timing of the onset of ipsilateral activity precludes its role in response initiation. Rather, this activity may indicate reflex-like activation of the unaffected motor system to compensate for possible failure of the affected hand.

Aged↗

PubMed2003

On the translation of some stimulus features to response force.

Romaiguère et al. (1993) reported an stimulus-response (S-R) experiment in which the participants had to respond to bright or dim stimuli by pressing a key strongly or weakly. Reaction time (RT) for a compatible S-R assignment (bright-strong; dim-weak) was substantially shorter than for an incompatible S-R assignment (dim-strong; bright-weak). This effect was explained as a direct translation of stimulus intensity to response force (RF). In the present study, we looked for other stimulus features that could be directly transferred to RF. We investigated stimulus size (large/small), vertical location (above/below), and brightness (bright/dim). Delays of RT for incompatible trials were found in case of brightness and size, but not location. In a second experiment, we tested whether such a direct translation might even cause changes of spontaneous RF. Without being instructed about RF, participants made simple reactions to stimuli which differed either in location, size or brightness. Indeed, stimulus size affected RF: larger stimuli were associated with stronger responses. In contrast, brightness had no effect. Thus, we replicated and extended Romaiguère et al.'s (1993) finding. However, the direct-translation account for RF variations received only partial support from our data.

Adolescent↗

PubMed2002

Effects of stimulus-induced saccades on manual response times in healthy elderly and in patients with right-parietal lesions.

Response delays of hemi-neglect patients to invalidly cued left targets in Posner's visual cueing task have been interpreted as reflecting disorders of covert attention, although shifts of overt attention have so far not been systematically measured in patients performing this task. Therefore, we measured saccades (i.e., fast goal-directed eye movements) induced by cues and targets in this task in ten patients with lesions of the right posterior parietal cortex and in age-matched healthy subjects. Participants were not aware that their saccades were studied. Of greatest interest was whether the presence or absence of saccades would modify the patients' response delay with invalidly cued left targets. In both groups, saccades occurred in many trials, key-press responses were slower in saccade trials than in no-saccade trials, and the delay by invalid cues was larger in saccade trials. The patients' responses were in particular delayed if preceded by saccades to the left. Their delay to invalidly cued left targets almost doubled (144 ms vs 76 ms) when only saccade trials were analyzed compared to when only no-saccade trials were analyzed. Thus, overt shifts (saccades) have a similar but larger effect on manual responses than covert shifts of attention. In particular, overt shifts make a considerable contribution to the patients' pathological delay of responses to invalidly cued left targets.

Aged↗

PubMed2002

Aging and the Simon task.

A visual Simon task was used to study the influence of aging on visuospatial attention and inhibitory control processes. Responses were much slower for elderly than for young participants. The delay in trials in which stimulus and response side did not correspond as compared to when they did correspond (the Simon effect) was larger for older people, even after correcting for general slowing due to aging. The slowing of responses reflected a slowing of internal processing, as indicated by progressively larger delays of the peak latencies of the N1, the posterior contralateral negativity (PCN), and P3. A comparison between the amplitudes of the PCN and early lateralized readiness potential (pre-LRP) indicated that transmission from posterior sites (PCN) to the motor cortex may be affected by age. The data support the view that aging affects an inhibitory process that controls direct visuomotor transmission.

Adult↗

PubMed2002

Traces left on visual selective attention by stimuli that are not consciously identified.

Briefly presented information, even if unidentifiable, may speed or delay required responses to following events. It has been assumed that this priming of the motor system may occur without affecting attention to priming and following stimuli. In contrast to this notion, the present study reports that such unidentified stimuli have effects on a physiological indicator of the attentional system. A lateral posterior electroencephalogram component was evoked by laterally presented relevant shapes, reflecting shifts of attention to those shapes. This component was absent, however, when the relevant shape was preceded by a similar shape at the same location, even if this shape was completely masked by metacontrast. The attentional shift evidently became unnecessary in this situation. Thus, unidentifiable information may leave some trace for attention-controlled selection of the following event.

Attention↗