Christian Erdmann

Motor Memory Consolidation in Sleep Shapes More Effective Neuronal Representations

Learning a motor skill involves a latent process of consolidation that develops after training to enhance the skill in the absence of any practice and crucially depends on sleep. Here, we show that this latent consolidation during sleep changes the brain representation of the motor skill by reducing overall the neocortical contributions to the representation. Functional magnetic resonance brain imaging was performed during initial training and 48 h later, at retesting, on a sequential finger movement task with training followed by either a night of regular sleep or sleep deprivation. An additional night of sleep for all subjects served to rule out unspecific effects of sleep loss at retrieval testing. Posttraining sleep, but not sleep deprivation, led to improved motor skill performance at retrieval. This sleep-dependent improvement was linked to greatly reduced brain activation in prefrontal, premotor, and primary motor cortical areas, along with a stronger involvement of left parietal cortical regions. Our findings indicate that storing a motor skill during sleep reorganizes its brain representation toward enhanced efficacy.

The anterior cingulate cortex contains distinct areas dissociating external from self-administered painful stimulation: a parametric fMRI study.

&NA; The anterior cingulate cortex (ACC) has a pivotal role in human pain processing by integrating sensory, executive, attentional, emotional, and motivational components of pain. Cognitive modulation of pain‐related ACC activation has been shown by hypnosis, illusion and anticipation. The expectation of a potentially noxious stimulus may not only differ as to when but also how the stimulus is applied. These combined properties led to our hypothesis that ACC is capable of distinguishing external from self‐administered noxious tactile stimulation. Thermal contact stimuli with noxious and non‐noxious temperatures were self‐administered or externally applied at the resting right hand in a randomized order. Two additional conditions without any stimulus‐eliciting movements served as control conditions to account for the certainty and uncertainty of the impending stimulus. Calculating the differences in the activation pattern between self‐administered and externally generated stimuli revealed three distinct areas of activation that graded with perceived stimulus intensity: (i) in the posterior ACC with a linear increase during external but hardly any modulation for the self‐administered stimulation, (ii) in the midcingulate cortex with activation patterns independent of the mode of application and (iii) in the perigenual ACC with increasing activation during self‐administered but decreasing activation during externally applied stimulation. These data support the functional segregation of the human ACC: the posterior ACC may be involved in the prediction of the sensory consequences of pain‐related action, the midcingulate cortex in pain intensity coding and the perigenual ACC is related to the onset uncertainty of the impending stimuli.

Cortical mechanisms of smooth pursuit eye movements with target blanking. An fMRI study.

Smooth pursuit eye movements are evoked by retinal image motion of visible moving objects and can also be driven by the internal representation of a target due to extraretinal mechanisms (e.g. efference copy). To delineate the corresponding neuronal correlates, functional magnetic resonance imaging at 1.5 T was applied during smooth pursuit at 10 °/s with continuous target presentation and target blanking for 1 s to 16 right‐handed healthy males. Eye movements were assessed during scanning sessions by infra‐red reflection oculography. Smooth pursuit performance was optimal when the target was visible but decreased to a residual velocity of about 30% of the velocity observed during continuous target presentation. Random effects analysis of the imaging data yielded an activation pattern for smooth pursuit in the absence of a visual target (in contrast to continuous target presentation) which included a number of cortical areas in which extraretinal information is available such as the frontal eye field, the superior parietal lobe, the anterior and the posterior intraparietal sulcus and the premotor cortex, and also the supplementary and the presupplementary eye field, the supramarginal gyrus, the dorsolateral prefrontal cortex, cerebellar areas and the basal ganglia. We suggest that cortical mechanisms such as prediction, visuo‐spatial attention and transformation, multimodal visuomotor control and working memory are of special importance for maintaining smooth pursuit eye movements in the absence of a visible target.

Differential cerebellar activation related to perceived pain intensity during noxious thermal stimulation in humans: a functional magnetic resonance imaging study

Little is known about the cerebellar involvement in pain processing in spite of the fact that the cerebellum probably plays a crucial role in pain-related behavior. Using functional magnetic resonance imaging we examined the differential cerebellar activation in 18 healthy subjects in relation to their perceived pain-intensity of noxious and non-noxious thermal stimuli. In contrast to non-noxious (40 degrees C) stimuli, noxious (48.5 degrees C) stimuli revealed activation in the deep cerebellar nuclei, anterior vermis and bilaterally in the cerebellar hemispheric lobule VI. With the same noxious stimulus (48.5 degrees C) there was differential cerebellar activation depending on the perceived pain intensity: high pain intensity ratings were associated with activation in ipsilateral hemispheric lobule III-VI, deep cerebellar nuclei and in the anterior vermis (lobule III). This differential cerebellar activation pattern probably reflects not only somatosensory processing but also perceived pain intensity that may be important for cerebellar modulation of nociceptive circuits.

Cerebellar activation in opsoclonus An fMRI study

It is controversial whether opsoclonus is a cerebellar or brainstem disorder. Two patients whose opsoclonus largely disappeared on eye closure underwent fMRI. A comparison of these two states revealed neither vermal nor brainstem activation but rather a bilateral activation in the deep cerebellar nuclei in excess of what the authors found in healthy subjects. The results support a crucial role of the fastigial nucleus in opsoclonus.

Parametric modulation of cortical activation during smooth pursuit with and without target blanking. an fMRI study.

Smooth pursuit eye movements (SPEM) are performed to track slowly moving visual targets and are accompanied by saccades whenever foveal representation is lost. In the present study, we correlated the cerebral activation as assessed by functional magnetic resonance imaging with parameters of eye movement performance in order to determine the cortical areas involved in the retinal and extraretinal processing of maintaining smooth pursuit velocity (SPV) and generating saccades in 16 healthy males. The stimulus consisted of a target moving at a constant velocity of 10 degrees/s with and without target blanking. During constant target presentation, SPV was positively correlated with the BOLD signal in the right V5 complex and negatively correlated with the BOLD response in the left dorsolateral prefrontal cortex (DLPFC). In the condition with target blanking, additional negative correlations with SPV were found in the left frontal eye field (FEF), the left parietoinsular vestibular cortex (PIVC) and the left angular gyrus. Saccadic frequency was negatively correlated with activations of the right mesial intraparietal sulcus (IPS) during both conditions and the right premotor area during continuous target presentation. We conclude that V5 is directly related to the maintenance of an optimal smooth pursuit velocity during visual feedback, whereas the FEF, PFC, angular gyrus and PIVC are involved in reconstitution and prediction whenever SPV decreases, especially during maintenance of smooth pursuit in the absence of a visual target. Furthermore, we suggest that parietal areas are related to the suppression of saccades during smooth pursuit.

Activation of cerebellar hemispheres in spatial memorization of saccadic eye movements: an fMRI study.

What mechanisms allow us to direct a precise saccade to a remembered target position in space? The cerebellum has been proposed to be involved not only in motor and oculomotor control, but also in perceptual and cognitive functions. We used functional MRI (Echoplanar imaging at 1.5 T) to investigate the role of the cerebellum in the control of externally triggered and internally generated saccadic eye movements of high and low memory impact, in six healthy volunteers. Memory‐guided saccades to remembered locations of 3 targets (triple‐step saccades) in contrast to either central fixation or to visually guided saccades activated the cerebellar hemispheres predominantly within lobuli VI‐crus I. The same areas were activated when an analogous visuospatial working memory task was contrasted to the triple‐step saccades. Visually guided saccades activated the posterior vermis and the triple‐step saccades, contrasted to the working memory task, activated predominantly the posterior vermis and paravermal regions. Our data confirm the primary involvement of the posterior vermis for visually‐triggered saccadic eye movements and present novel evidence for a role of the cerebellar hemispheres in the mnemonic and visuospatial control of memory‐guided saccades. Hum. Brain Mapp. 22:155–164, 2004.

Neural activity related to self- versus externally generated painful stimuli reveals distinct differences in the lateral pain system in a parametric fMRI study

Self‐generated sensory stimulation can be distinguished from externally generated stimulation that is otherwise identical. To determine how the brain differentiates external from self‐generated noxious stimulation and which structures of the lateral pain system use neural signals to predict the sensory consequences of self‐generated painful stimulation, we used functional magnetic resonance imaging to examine healthy human subjects who received thermal‐contact stimuli with noxious and non‐noxious temperatures on the resting right hand in random order. These stimuli were internally (self‐generated) or externally generated. Two additional conditions served as control conditions: to account for stimulus onset uncertainty, acoustic stimuli preceding the same thermal stimuli were used with variable or fixed delays but without any stimulus‐eliciting movements. Whereas graded pain‐related activity in the insula and secondary somatosensory cortex (SII) was independent of how the stimulus was generated, it was attenuated in the primary somatosensory cortex (SI) during self‐generated stimulation. These data agree with recent concepts of the parallel processing of nociceptive signals to the primary and secondary somatosensory cortices. They also suggest that brain areas that encode pain intensity do not distinguish between internally or externally applied noxious stimuli, i.e., this adaptive biological mechanism prevents harm to the individual. The attenuated activation of SI during self‐generated painful stimulation might be a result of the predictability of the sensory consequences of the pain‐related action. Hum Brain Mapp, 2006.

Emotional reactivity to threat modulates activity in mentalizing network during aggression

Aggression is a common response to provocation, albeit with considerable interindividual differences. In this fMRI study, we investigated emotional reactivity to threat as possible link between provocation and aggression, as well as the neural correlates of this relationship. We hypothesized that emotional reactivity, measured as fear potentiation (FP) of the startle response, would be negatively associated with aggressive behavior and would modulate neural activity during an aggressive interaction. In 30 healthy female participants, FP was measured as the difference between blink amplitudes while watching threatening vs neutral pictures. Participants subsequently engaged in a variant of the Taylor Aggression Paradigm (TAP), while being scanned. During the TAP, participants selected a punishment level for either a highly provoking or a nonprovoking opponent. There was no difference in aggressive behavior between participants high and low in FP. However, we found a negative correlation between FP and the neural provocation effect in several regions of a network previously associated with mentalizing including the medial prefrontal cortex, precuneus and the temporo-parietal junction. Independently of the FP variability, aggressive behavior correlated with the provocation effect on activity in the caudate nucleus. Our results indicate that during a provocative confrontation, high emotional reactivity to threat suppresses recruitment of the mentalizing network.

Cerebellar neural responses related to actively and passively applied noxious thermal stimulation in human subjects: a parametric fMRI study ☆

Cerebellar activation is consistently found during noxious stimulation but little is known about its pain-related specificity. Under natural circumstances noxious stimuli are actively or passively delivered with concomitant tactile sensory stimulation. Using fMRI we therefore studied pain-related cerebellar activation with innocuous and noxious thermal stimuli in a parametric design taking motor execution as confounding factor into account. With respect to psychophysical pain ratings anterior vermal and ipsilateral hemispheric lobule VI activation was parametrically modulated for stimulus intensity in actively but not in passively elicited thermal stimulation. The cerebellum seems to be capable of distinguishing active from passive painful stimuli.