Wilfried Lang

Mental representations of movements. Brain potentials associated with imagination of eye movements

OBJECTIVE Current research in motor imagery is focused on similarities between actual and imagined movements on a central and a peripheral level of the nervous system. The present study measured slow cortical potentials (DC-potentials) during execution and internal simulation of memorized saccadic eye movements. METHODS In 19 healthy righthanded subjects DC-potentials were recorded from 28 electrodes during execution and during imagination of a sequence of memorized eye movements during a visual imagery condition. RESULTS Both oculomotor conditions showed a similar global level and similar topography of performance related DC-potentials, both strongly differed from the visual imagery condition and were lateralized to the left hemisphere. CONCLUSION This study therefore supports the hypothesis that cortical brain structures responsible for execution and imagination of memorized saccadic eye movements are similar. The observed left hemispheric lateralization is in contrast to a previous study using bimanual movements. This discrepancy is discussed in relation to recent observations in apractic patients with parietal lesions.

Supplementary motor area activation while tapping bimanually different rhythms in musicians

SummaryIn 15 musicians, cortical DC-potentials were recorded from the scalp before and during the execution of bimanual motor sequences. Subjects (Ss) either tapped with their two index fingers in synchrony (quavers against quavers; “2 against 2”) or they tapped quavers against triplets (“2 against 3”). Either the right or the left finger started tapping the quavers (onset time t1), after about 4 s the other finger joined in (t2) either with quavers as well (easy rhythm) or with triplets (difficult rhythm). Ss were free to start the sequences, i.e. to determine the onset times t1 and t2. Shifts of cortical DC potentials were averaged twice; (1) time-locked to t1 and (2) time-locked to t2. When moving in synchrony (easy rhythm) DC-potential shifts and maps of radial current densities across the scalp indicated activations of the two primary motor cortices (MI). When bimanually tapping different rhythms, there was not only an activation of MI cortices, but in addition a very large activation of the mesial, central cortex was observed. It is suggested that this cortical area which mainly contains the supplementary motor area (SMA) has the function of controlling the initiations of movements in the difficult sequence which have to fit into a very precise timing plan. Interestingly, activation of the mesial, central cortex preceded the actual performance of the difficult rhythm by about 4 s. This finding indicates that the preparatory set differs between the two tasks.

Neuroimage of Voluntary Movement: Topography of the Bereitschaftspotential, a 64-Channel DC Current Source Density Study☆

The Bereitschaftspotential (BP) was recorded at 56 scalp positions when 17 healthy subjects performed brisk extensions of the right index finger. Aim of the study was to contribute to our understanding of the physiology underlying the BP and, in particular, to specify the situation at BP onset. For this purpose, the spatial pattern of the BP was analyzed in short time intervals (35 and/or 70 ms) starting 2.51 s before movement onset. For each time segment a spherical model of the BP was calculated by using spline interpolation. Then the spatial distribution of the electric potential at the scalp surface was transformed into a spatial distribution of current source densities (CSD map). Onset times of the BP and onset times of initial CSD-activity ranged between 2.23 and 1.81 s before movement onset. We selected a time window between 1.6 and 1.5 s before movement onset in order to analyze the spatial CSD pattern in each subject. In 10 subjects there was a significant current sink in the scalp area located over medial-wall motor areas (pre-SMA, SMA proper and anterior cingulate cortex: electrode positions C1, C2, FCz, Cz) in the absence of a significant current sink over the primary motor cortex (MI: electrode positions C3, CP3, and CP5). In three subjects significant current sinks were present at both sites and in another three subjects a current sink only over the lateral motor cortex was observed. In one subject no significant current sinks were measured. It is concluded that there is a large group of subjects (13/17) in whom BP at onset is associated with a current sink over medial-wall motor areas. At a later time interval (0.6 to 0.5 s before movement onset), significant current sinks were found in 13 subjects in medial and in 10 subjects in lateral recordings. These data were considered to be consistent with the hypothesis that, at least in a majority of subjects, medial-wall motor areas are activated earlier than lateral motor areas when organizing the initiation of a simple self-paced movement. Surface-recordings of the EEG do not allow further specification of cortical areas, which contribute to the current sinks. But in context with the current literature of the electrophysiology of nonhuman primates and of brain imaging in humans it is suggested that SMA and anterior cingulate cortex contribute to the current sink, the fronto-central midline, and that the primary motor cortex (MI) contributes to the current sink in the scalp area, which is located above MI and closely posterior to it.

On the functionality of the visually deprived occipital cortex in early blind persons

In early blind mammals, the deprived visual cortex undergoes anatomical and functional alterations. Its functional role was investigated in the early human blind by using patterns of cortical activation as measured by scalp-recorded event-related slow negative DC potential shifts. The blind showed higher occipital negativity than did sighted persons both during a tactile reading task and a non-reading tactile control task. Results point to a possible role for the blinds visual cortex in tactile processes.

Negative cortical DC shifts preceding and accompanying simultaneous and sequential finger movements

SummaryCortical DC shifts preceding and accompanying the execution of five different bimanual motor tasks were analysed in 20 subjects. All tasks required repetitive flexions and extensions of the two forefingers for a period of at least six seconds. The temporal and spatial structures organization varied in the different tasks: (1) Simultaneous agonistic performance (forefinger flexion on both sides), (2) simultaneous antagonistic performance (e.g. flexion of the right, extension of the left forefinger), (3) sequential agonistic performance, (4) sequential antagonistic performance, (5) uncoordinated flexions and extensions of the two forefingers. Compared to (1) and (2), conditions (3) and (4) included a temporal delay between the performance of the two forefingers; compared to (1) and (3), conditions (2) and (4) required the subjects to perform movements of opposite directions with their two forefingers. Effects of the temporal factor (T; simultaneous vs. sequential) and the spatial factor (S; agonistic vs. antagonistic) on cortical DC shifts were investigated. The voluntary initiation of each motor task was preceded by a Bereitschaftspotential (BP). The performance of the complex tasks (1–4) was accompanied by a slow negative DC potential shift (N-P). In general, the BP did not differ depending on the temporal or spatial structures of the tasks (1–4). However, amplitudes of N-P (i.e. during tasks) were influenced by the temporal factor with significantly larger amplitudes in sequential than in simultaneous tasks. This difference was not a global phenomenon in all recordings but was selectively found in the recordings over the fronto-central midline. The spatial factor had no influence on N-P. It is suggested that the timing-dependent increase of N-P reflects greater activation of the fronto-central midline including the supplementary motor area (SMA) in sequential as compared to simultaneous movements. Furthermore, the data substantiate the hypothesis that the fronto-central midline (including the SMA) is rather involved in the temporal than the spatial coordination of bimanual motor tasks.

Carotid artery stenting: effect of learning curve and intermediate-term morphological outcome.

Purpose: To assess the impact of learning on the rate of success and complications of carotid stenting in a single-center, one-operator series and prospectively follow a patient cohort with regard to restenosis. Methods: In 303 patients (mean age 70 ± 8.8 years), 320 internal carotid arteries (ICA) were treated with carotid stenting for stenoses ≥70%. Four groups of 80 consecutive interventions were compared with regard to primary technical success and periprocedural complications. Stent patency in follow-up was assessed using duplex scanning. Results: Stenting was successful in 298 (93%) arteries. The combined neurological complications (transient ischemic attacks and all strokes) and 30-day death rate was 8.2% (n = 25), but the all stroke and 30-day death rate was 3.0% (n = 9). A significant reduction in the frequency of neurological complications after the initial 80 interventions was observed (p = 0.03), but technical success was not appreciably improved with increasing experience thereafter. Over a median 12 months (interquartile range 6 to 24), cumulative patency rates were 91%, 90%, and 91% at 6, 12, and 36 months, respectively. Conclusions: Elective carotid stenting can be performed with excellent technical success, an acceptable frequency of periprocedural complications, and good intermediate-term patency. However, our findings suggest that a larger number of interventions should be performed to overcome the negative effects of the initial learning phase.

High resolution spatiotemporal analysis of the contingent negative variation in simple or complex motor tasks and a non-motor task

OBJECTIVES Since the characteristics of the Bereitschaftspotential (BP) - voluntary movement paradigm of internally-driven movements - have been established recently by our group using high resolution DC-EEG techniques, it was of great interest to apply similar techniques to the other slow brain potential--contingent negative variation (CNV) of externally-cued movements--with the same motor tasks using the same subjects. METHODS The CNV for simple bimanual sequential movements (task 1), complex bimanual sequential movements (task 2) and a non-motor condition (task 3) was recorded on the scalp using a 64 channel DC-EEG in 16 healthy subjects, and the data were analyzed with high resolution spatiotemporal statistics and current source density (CSD). RESULTS (1) The CNV was distributed over frontal, frontocentral, central and centroparietal regions; a negative potential was found at the frontal pole and a positive potential was found over occipital regions. (2) CNV amplitudes were higher for task 2 than for task 1, and there was no late CNV for task 3. (3) A high resolution spatiotemporal analysis revealed that during the early CNV component, statistical differences existed between the motor tasks (tasks 1 and 2) and the non-motor task (task 3), which occurred at frontocentral, central, centroparietal, parietal and parieto-occipital regions. During the late CNV component, additional significant differences were found not only between the motor tasks and the non-motor task but also between motor task 1 and task 2 at frontocentral, central and centroparietal regions. (4) Comparison of the CNV between the frontomesial cortex (situated over the supplementary/cingulate areas, SCMA) and both lateral pre-central areas (situated over the primary motor areas, MIs) showed that there was no statistically significant difference between the two cortical motor areas except for the early CNV. (5) Comparison of the CNV between the 3 tasks over the cortical motor areas showed that there were significant differences between the motor tasks and the non-motor task regarding the auditory evoked potential (AEP) and the early CNV component, and between all 3 tasks in the late CNV, the visual evoked potential (VEP(2)) and the N-P component. (6) The ranges and the densities of the CSD maps were larger and higher for complex than for simple tasks. The current sinks of the AEP and the early CNV were located at Fz, the late CNV at FCz and surrounding regions. As to be expected, current sources of the VEPs were located at the occipital lobes. The CNV was a current sink (negative) except for the VEPs main component which was a current source (positive). CONCLUSIONS (1) The CNV topography over the scalp varied with the complexity of motor tasks and between motor and non-motor conditions. (2) The origin of the early CNV may rest in the frontal lobes, while the late CNV may stem from more extensive cortical areas including SCMA, MIs, etc. (3) The late CNV component is not identical with the BP.

Effect of pretreatment with statins on the severity of acute ischemic cerebrovascular events

OBJECTIVE Treatment with statins reduces the risk of ischemic stroke among patients at increased risk for vascular disease. Recent experimental data suggest neuroprotective properties of statins in acute cerebral ischemia. We investigated whether a premedication with statins is associated with a better outcome in patients with acute ischemic cerebrovascular events. METHODS Within a cross-sectional study, nested in a cohort we identified 1691 patients with a recent ischemic stroke or transient ischemic attack. Clinical severity of the vascular event was evaluated by the modified Rankin Scale (mRS) after 1 week. By means of multivariate logistic regression modeling, we determined the influence of prior statin use on stroke severity with adjustment for potential confounding factors. RESULTS Severe stroke, defined as a modified Rankin Scale of 5 or 6 (n=231; 14%), was less frequent in patients receiving statin treatment before the event (6% vs. 14%, OR=0.37; 95% CI 0.19 to 0.74; p=0.004). This association remained significant after adjustment for confounding factors. We found a significant interaction between the presence of diabetes and the effect of pretreatment with statins on stroke outcome. Of the patients with diabetes, none of those on statin treatment but 16% of those without a statin had a bad outcome. After exclusion of the group of diabetic patients with prior statin medication, the protective effect was reduced and not statistically significant anymore. CONCLUSIONS Pretreatment with statins seems to be associated with reduced clinical severity in patients with acute ischemic cerebrovascular events, particularly in patients with diabetes.

Headache at Stroke Onset in 2196 Patients With Ischemic Stroke or Transient Ischemic Attack

Background and Purpose— Headache is a common symptom in acute ischemic and hemorrhagic stroke, but many aspects of its association with other clinical factors are controversial. Methods— We analyzed characteristics of headache symptoms at stroke onset and associations between headache at stroke onset and at several clinical parameters in 2196 patients experiencing ischemic stroke or transient ischemic attack within a multicenter hospital-based stroke registry. Results— Five hundred eighty-eight (27%) patients experienced headache at stroke onset. In a multivariate analysis, headache at stroke onset was positively associated with female sex, history of migraine, younger age, cerebellar stroke (but not with other brain stem locations), and blood pressure values on admission <120 mm Hg systolic and <70 mm Hg diastolic. It showed no significant association with stroke severity measured by the modified Rankin Scale at days 5 to 7 after the event, presumed etiology, or time of day. Conclusions— Our results, derived from a large number of systematically documented patients with acute ischemic cerebrovascular events, show no association of headache with stroke etiology or outcome. Our results indicate that the previously described association of headache with vertebrobasilar stroke is mainly because of its association with cerebellar stroke. We could confirm previously described associations of headache at stroke onset with younger age and a history of migraine, implicating a careful evaluation of young patients with a focal neurological deficit and a history of migraine to avoid misclassification as “complicated migraine.”

Negative cortical DC shifts preceding and accompanying simple and complex sequential movements

SummaryNegative cortical DC shifts preceding and accompanying the execution of four different motor tasks were analysed in 18 subjects (Ss): Repetitive flexions and extensions of the forefinger had to be performed either by the right (1) or the left (2) hand. This simple motor task was compared to a complex one in which flexions and extensions of forefinger and hand had to be alternated in a fixed sequence. The complex task had either to be performed by the right (3) or the left (4) hand. Thus, the four conditions differed in the side of the performing hand (right/left) and in task-complexity (simple/complex). After its voluntary initiation, each task had to be performed for at least a period of six seconds. A Bereitschaftspotential (BP) preceded the voluntary initiation of the movement. Task-performance was accompanied by a negative DC shift called a performance-related negativity (N-P). Amplitudes of BP and N-P were compared by analysis of variance (ANOVA) using the factors “performing hand” (right/left) and “task-complexity” (simple/complex). “Performing hand” had significant effects on N-BP and N-P in C3* and C4* (positioned over the primary motor cortex) but did not influence mid-central (Cz*), frontal (F3, Fz, and F4) or parietal (P3, Pz, P4) recordings. “Task-complexity” had significant effects on N-P in mid-central (Cz*, C1*, C2*) and parietal (P3, Pz) recordings with higher negativity for complex movements. Recordings in C3* and C4* did not vary with “task complexity”. Dissociative effects of “performing hand” and “task-complexity” indicate that movement-related DC-potential shifts in C3*/ C4* can functionally be separated from those recorded in Cz*. Variations depending on the specific properties of the tasks were found to be larger during performance than during preparation of the task.