Rolf Verleger

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.

Evidence for an Integrative Role of P3b in Linking Reaction to Perception

Hypotheses about the P3 component of the event-related EEG potential have usually assumed that P3b reflects some processing independent from organizing the response. In contrast, the notion that P3b is related to a decision process implies some mediating function between stimulus and response. If P3b does indeed reflect the link between perceptual processing and response preparation (1) amplitudes should be as large in response-locked averages as in stimulus-locked averages, (2) this should be true independent of response speed, for separate subaverages of slow and fast responses, and (3) latencies should vary across response speed both in stimulus-locked and in response-locked averages. These hypotheses were tested in data evoked by visual and auditory stimuli in choice-response tasks. All three predictions were confirmed. In contrast to this balanced relation to perception and responding, fronto-central P3 with auditory stimuli was stimulus-related and, for comparison, the peak amplitudes of both the response-force and of the lateralized readiness potential were response-related. We conclude that P3b reflects a process that mediates between perceptual analysis and response initiation, possibly monitoring whether the decision to classify some stimulus is appropriately transformed into action.

Development of the EEG of school-age children and adolescents. I. Analysis of band power

Development in quantitative EEG parameters is studied for a sample of 158 normal children and adolescents aged 6-17 years. This is of interest both for increasing basic knowledge of human neurophysiology and for obtaining age standardized norms, useful in clinical research and applications. After selecting an appropriate epoch and correcting for EOG artifacts, the EEG at 8 derivations was submitted to spectral analysis in order to extract broad-band parameters in absolute and relative power. Change in EEG band power across age was quantified by polynomial regression analysis. This opened automatically the possibility to obtain age-standardized EEG norms. Development was for most EEG parameters non-linear, with more pronounced changes for absolute than for relative power. No sex differences and no pubertal spurt could be identified in contrast to most somatic quantities. A detailed statistical analysis revealed, however, that this might be due to using cross-sectional data. All bands except for alpha 2 decreased in absolute power, whereas the fast bands increased and the slow bands decreased in relative power. Strong evidence was found for a substituting process between theta activity and fast alpha activity.

Validity and boundary conditions of automatic response activation in the Simon task

Three experiments were conducted to determine whether spatial stimulus-response compatibility effects are caused by automatic response activation by stimulus properties or by interference between codes during translation of stimulus into response coordinates. The main evidence against activation has been that in a Simon task with hands crossed, responses are faster at the response location ipsilateral to the stimulus though manipulated by the hand contralateral to the stimulus. The experiments were conducted with hands in standard and in crossed positions and electroencephalogram measures showed coactivation of the motor cortex induced by stimulus position primarily during standard hand positions with visual stimuli. Only in this condition did the Simon effect decay with longer response times. The visual Simon effect appeared to be due to specific mechanisms of visuomotor information transmission that are not responsible for the effects obtained with crossed hands or auditory stimuli.

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.

Development of the EEG of school-age children and adolescents. II: Topography

Topographic aspects of EEG development of normal children and adolescents from 6 to 17 years are investigated with respect to various spectral parameters. The topographic distribution of spectral band power does not change between hemispheres across age. Changes take place, however, in the antero-posterior dimension. For the bands theta, alpha 1 and alpha 2 (and less so for delta) maturation starts at posterior derivations and ends at anterior derivations. For the band beta 2 (and to some extent also for beta 1), development progresses from Cz to Pz and further to occipital, lateral, central and frontal derivations. Principal component analysis (PCA) leads to a more parsimonious and better interpretable description of broad-band power and of its topographic distribution. Broad-band coherences increase with age, though to a modest degree. The different magnitudes of coherence between different regions can be largely accounted for by the interelectrode distances. Coherences, too, can be described in a more parsimonious and better interpretable way via PCA. The 3 components extracted reflect firstly the overall level of coherence, secondly the coherences of the occipital regions with all other regions and thirdly antero-posterior versus left-right coherences.

Qualitative differences between conscious and nonconscious processing? On inverse priming induced by masked arrows

In general, both consciously and unconsciously perceived stimuli facilitate responses to following similar stimuli. However, masked arrows delay responses to following arrows. This inverse priming has been ascribed to inhibition of premature motor activation, more recently even to special processing of nonconsciously perceived material. Here, inverse priming depended on particular masks, was insensitive to contextual requirements for increased inhibition, and was constant across response speeds. Putative signs of motor inhibition in the electroencephalogram may as well reflect activation of the opposite response. Consequently, rather than profiting from inhibition of primed responses, the alternative response is directly primed by perceptual interactions of primes and masks. Thus there is no need to assume separate pathways for nonconscious and conscious processing.

The instruction to refrain from blinking affects auditory P3 and N1 amplitudes

Often subjects have been instructed to refrain from blinking lest their evoked EEG potentials should be distorted. We studied whether these very instructions have any impact on P3 amplitude. Two tones were presented in random order, and subjects had to count the high-pitched tones. Half the subjects were instructed not to blink, whereas this instruction was omitted for the other subjects. Target tones evoked larger P3s than non-targets in the latter group but not in the former, in particular not in those subjects that actually blinked rarely. The groups also differed in their N1 amplitudes. These findings might be relevant to P3 studies working with patients and controls: the harder some frequently blinking subjects try to refrain from blinking, the smaller might become their P3 amplitudes. Omitting the instruction and using off-line blink subtraction procedures seems a viable alternative. This study was actually motivated by discrepant findings on the effects of the preceding tone sequence on P3. These discrepancies could be largely resolved by the instructional variable, in conjunction with different tone intensities. It is suggested that subjects who are discouraged from blinking try to protect themselves against the arousing effects of stimuli.

Spatiotemporal overlap between brain activation related to saccade preparation and attentional orienting

Recent brain imaging studies provided evidence that the brain areas involved with attentional orienting and the preparation of saccades largely overlap, which may indicate that focusing attention at a specific location can be considered as an unexecuted saccade towards that location (i.e. the premotor theory of attention). Alternatively, it may be proposed that attentional orienting is simply relevant for preparing saccades, but the two processes may also be completely unrelated. In two experiments, we examined temporal activation of brain areas by measuring the electroencephalogram. Central cues indicated the likely side (left or right) at which a to-be-attended target would occur, or to which a saccade had to be prepared. Cue direction-related activity was determined, time-locked to cue onset. In addition, in our second experiment, delayed saccades had to be carried out, which allows to focus on processes strongly related to saccade execution. In nearly all tasks, an early directing attention negativity (EDAN), an anterior directing attention negativity (ADAN), and a late directing attention positivity (LDAP) were observed, time-locked to cue onset. Source analyses supported the view that this activity probably originates from areas within the ventral intraparietal sulcus (vIPS) and the frontal eye fields (FEF). The saccade-locked analysis also indicated that the FEF plays an important role in triggering saccades, but the role of vIPS appears to be minimal. The latter finding disfavors the premotor theory of attention, as it suggests that the relation between attention and action is less direct.

On the reasons for the delay of P3 latency in healthy elderly subjects

The P3 component reaches its peak later in elderly subjects than in young subjects. The aim of this study was to repeat this finding in the usual auditory oddball task and to look for reasons for the delay by analysing other components and by applying another task, the visual Push/Wait task. It was found in the oddball that the age delay was present for mismatch negativity already but further increased until P3s peak. In the Push/Wait task, the size of the age delay was independent of another delay caused by reduced visual intensity of the stimuli. Further, the age delay had its onset after the occipital P140 component whereas the intensity delay was present before this component. Within the elderly, P3 latencies correlated between the auditory and the visual tasks, and the common factor extracted from both latencies correlated with a test of short-term memory span. It is concluded that the age delay of P3 is not due to a delay of perceptual encoding but perhaps due to delayed memory processes in the elderly. As usual, P3 amplitudes were larger and more parietally focussed in the young than in the elderly. Possible differences in motivation might account for this finding.