Impaired working-memory after cerebellar infarcts paralleled by changes in BOLD signal of a cortico-cerebellar circuit.

A considerable body of evidence supports the notion that cerebellar lesions lead to neuropsychological deficits, including impairments in working-memory, executive tasks and verbal fluency. Studies employing functional magnetic resonance imaging (fMRI) and anatomical tracing in primates provide evidence for a cortico-cerebellar circuitry as the functional substrate of working-memory. The present fMRI study explores the activation pattern during an n-back working-memory task in patients with an isolated cerebellar infarct. To determine each patient's cognitive impairment, neuropsychological tests of working-memory and attention were carried out. We conducted fMRI in nine patients and nine healthy age-matched controls while they performed a 2-back task in a blocked-design. In both groups we found bilateral activations in a widespread cortico-cerebellar network, consisting of the ventrolateral prefrontal cortex (BA 44, 45), dorsolateral prefrontal cortex (BA 9, 46), parietal cortex (BA 7, 40), pre-supplementary motor area (BA 6) anterior cingulate (BA 32). Relative to healthy controls, patients with isolated cerebellar infarcts demonstrated significantly more pronounced BOLD-activations in the precuneus and the angular gyrus during the 2-back task. The significant increase in activation in the posterior parietal areas of the cerebellar patients could be attributed to a compensatory recruitment to maintain task performance. We conclude that cerebellar lesions affect remote cortical regions that are part of a putative cortico-cerebellar network.

Effects of passive tactile co-activation on median ulnar nerve representation in human SI.

In animals simple passive co-activation causes a fusion and expansion of the involved cortical representations. We used passive tactile finger co-activation for 40 min to investigate cortical representational changes in the human somatosensory cortex. Magnetic source imaging revealed that the euclidean distance between median and ulnar nerve somatosensory evoked fields (SEF) was significantly reduced after application of 600 synchronous airpuff stimuli to the fingertips of four fingers. In the control experiment without co-activation no significant change in distance was observed. Perception threshold and spatial two-point discrimination were not affected by the synchronous stimulation. This is in contrast to blind three-finger Braille readers who frequently mislocalize stimuli applied to the reading fingers. This points to a lack of behavioural relevance or the short duration of co-activation.

Transcranial color-coded duplex sonography for detection of distal internal carotid artery stenosis.

BACKGROUND AND PURPOSE: Gradation of high-grade intracranial internal carotid artery (ICA) stenosis poses a challenge to noninvasive neurovascular imaging, which seems critical for angioplasty in the ICA segments C1 and C5. We investigated cutoff values of intracranial ICA stenosis for transcranial color-coded sonography (TCCS) and compared this method with the "gold standard," digital subtraction angiography (DSA). MATERIALS AND METHODS: Forty patients (mean age, 58.9 +/- 13.8 years) with intracranial ICA lesions were prospectively examined by using TCCS and DSA. Two standard TCCS coronal imaging planes were used to evaluate the intracranial ICA. In addition, a control group of 128 volunteers without cerebrovascular disease (mean age, 48.8 +/- 15.9 years) was investigated to establish standard velocity values. RESULTS: DSA confirmed 96 stenoses and 8 occlusions of the intracranial ICA in the study population. In 9% and 7% of cases, stenosis confined to the C1 or C5 segment was >50% and 70%, respectively. Receiver-operating curves demonstrated cutoff values for >70% stenosis in C1 when the peak systolic velocity (PSV) was >200 cm/s (specificity, 100%; sensitivity, 71%) or the C1/submandibular ICA index was >3 (specificity, 93%; sensitivity, 86%). CONCLUSIONS: TCCS is a reliable adjunctive method to detect and quantify significant stenosis of the intracranial ICA. The assessment of the C1/ICA index and peak systolic velocities maximizes the diagnostic accuracy of C1 stenosis to >70% when extracranial ICA stenosis coexists. Further studies need to be performed to compare the diagnostic accuracies of MR angiography and TCCS with that of DSA.

Differences in cortical activation during smooth pursuit and saccadic eye movements following cerebellar lesions.

Current evidence supports the proposal that the cerebellum mediates the activity of other brain areas involved in the control of eye movements. Most of the evidence so far has concentrated on the vermis and flocculi as the cerebellar agents of oculomotor control. But there is also evidence for an involvement of the cerebellar hemispheres in eye movement control. Straube et al. (Ann Neurol 42:891-898, 1997) showed that lateral hemispheric lesions affect initiation of smooth pursuit (SPEM) and saccadic eye movements. Ron and Robinson (J Neurophysiol 36:1004-1022, 1973) evoked smooth pursuit and saccadic eye movements by electrical stimulation of crus I and II, as well as in the dentate nuclei of the monkey. Functional MRI studies also provide evidence that the cerebellar hemispheres play a significant role in SPEM and saccadic eye movements. To clarify the role of the cerebral hemispheres in eye movement control we compared the eye movement related blood oxygen level dependent (BOLD) responses of 12 patients with cerebellar lesions due to stroke with those of an aged-matched healthy control group. Six patients showed oculomotor abnormalities such as dysmetric saccades or saccadic SPEM during the experiment. The paradigm consisted of alternating blocks of fixation, visually guided saccades and visually guided SPEM. A nonparametric random-effects group analysis showed a degraded pattern of activation in the patient group during the performance of SPEM and saccadic eye movements in posterior parietal areas putatively containing the parietal eye fields.

[Problems of emergency transfers of patients after a stroke. Results of a telemedicine pilot project for integrated stroke accommodation in southeast Bavaria (TEMPiS)]. / Problemfeld der Notfallverlegungen beim Schlaganfall. Ergebnisse des telemedizinischen Pilotprojekts zur integrierten Schlaganfallversorgung in Südostbayern (TEMPiS).

BACKGROUND: Specific stroke subtypes like subarachnoid hemorrhages or malignant brain infarcts require immediate interventions, but treatment options are offered mainly in specialized centers. For this reason, interhospital transfers from primary hospitals need to be done without delay. METHODS: The telemedic pilot project for integrative stroke care (TEMPiS) connects 2 stroke centers and 12 regional hospitals in Bavaria (Germany). Core elements are the implementation of stroke wards, telemedic consultation and improvement of emergency interhospital transfers. Organization of patient transports is offered by the central telemedic service. During the first 12 months of the continuing project all interhospital transfers initiated by the central telemedic service were prospectively documented. Emergency transports were analysed according to diagnosis, type of transport, distance and time delays. RESULTS: A total of 252 interhospital transfers were recommended in teleconsultations; finally 221 transports took place. Median total duration of transfers (including the necessary arrangements) was 134 min (interquartile range: 105-219) for intracerebral hemorrhages (N = 58), 138 min (95-157) for subarachnoid hemorrhages (N = 31), 161 min (100-230) for malignant infarcts (N = 22) and 147 min (109-180) for suspected basilar artery occlusion (N = 28). Time from admission in the primary hospital to initiation of interhospital transfer was 135 min (median; interquartile range: 86-172), transport time was 81 min (60-116). Helicopter transport did not save time for transfer distances up to 50 kilometres, compared to transport via ambulance (including assistance of hospital physicians). Transport using a special intensive care vehicle was much more time consuming because of the longer transport preparation time. CONCLUSION: Emergency transfers of stroke patients are time consuming. This may contribute to additional harm being done to severely ill patients. Faster organization and conduct of transports is required.