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At least 91 records · Page 5Linked to original sources
PubMed2002

Intrathalamic non-propagating generators of high-frequency (1000 Hz) somatosensory evoked potential (SEP) bursts recorded subcortically in man.

OBJECTIVES: Recently, bursts of high-frequency (1000 Hz) median nerve somatosensory evoked potential (SEP) wavelets were recorded subcortically near and inside the thalamus from deep brain electrodes implanted for tremor therapy. This study aimed to clarify whether these subcortical SEP bursts reflect evoked axonal volleys running in the thalamocortical radiation or a locally restricted intrathalamic response. METHODS: During deep brain electrode implantation, median nerve SEP were recorded in 7 patients sequentially along the subcortical stereotactic trajectory at sites +20 and +10 mm above the respective target nucleus (ventral intermediate thalamus or nucleus subthalamicus). Low- and high-frequency SEP components (corner frequency 430 Hz) were analyzed separately with respect to peak latency and amplitude as they changed along the recording trajectory. RESULTS: Individual wavelets of the subcortical 1000 Hz SEP burst showed fixed peak latencies independent from the depth of the electrode penetration; they increased markedly in amplitude with decreasing distance to the thalamus. In contrast, the amplitude gradient between the two recording sites was shallower for the low-frequency SEP component, which peaked earlier at the lower recording site. CONCLUSIONS: Subcortically recorded 1000 Hz SEP wavelet bursts predominantly reflect locally restricted near-field activity, presumably generated in the somatosensory relay nucleus. In contrast, the variable peak latency of the subcortical low-frequency component could reflect postsynaptic potentials sequentially evoked during passage of the lemniscal afferences curving through the thalamus and contributions from the thalamocortical radiation.

Aged↗
PubMed1999

Stability of high-frequency (600 Hz) components in human somatosensory evoked potentials under variation of stimulus rate--evidence for a thalamic origin.

The generators of spike-like high-frequency (600 Hz) wavelets superimposed on the primary cortical response (N20) in human median nerve somatosensory evoked potentials (SEP) have been localized anatomically both close to the primary somatosensory hand cortex and in deep axon segments of thalamo-cortical projection neurons. Here, N20 and 600 Hz burst components were functionally dissociated by varying the stimulus rate (1.5, 3, 6, 9 Hz). The N20 source amplitudes were significantly reduced at the higher stimulus rates. In contrast, the source amplitudes of the 600 Hz oscillations remained stable across all stimulus rates. This reflects different source origins, confirming a postsynaptic intracortical generation of the N20 component and provides further evidence for a presynaptic origin of the 600 Hz activity like repetitive neuronal population spikes conducted in deep and superficial segments of thalamo-cortical projection fibers.

Brain↗
PubMedDate not supplied

[REM sleep and recurrent corneal erosion--a hypothesis].

BACKGROUND: Recurrent corneal erosion typically occurs in the early morning. The cause of this nocturnal event has not yet been clarified. METHODS AND RESULTS: The literature explains corneal nutrition being diurnally normal and nocturnally deficient as follows: closed eyelids lead to relative corneal hypoxia with a temperature rise that impairs the physiological thermal circulation and thus obstructs the aqueous supply of amino acids and glucose to the cornea. The cornea is left with residual circulation and nutritional deficiency when the eyelids are closed. Corneal metabolism becomes glycolytic under anaerobic conditions, and the glycogen stores are depleted. Moreover, closed eyelids cause the pH of the tear film to decrease with increasing CO2 partial pressure. This results in failure of the pH-dependent epithelial pumps that promote corneal drainage when the eyelids are open during the day. The cornea thus becomes thicker at night. Rapid eye movements during frequent REM sleep phases in the second half of the night ameliorate the nocturnal nutritional deficiency of the healthy cornea by shaking the aqueous humor, which stagnates during sleep. CONCLUSION: The frequent recurrence of corneal erosion in the second half of the night may be due to a nocturnally intensified predisposing factor (nutritional deficiency of a previously damaged cornea) coinciding with a mechanical irritation (saccades during early morning REM sleep phases) in the case of a previously damaged corneal epithelium in conjunction with corneal dystrophy or microtraumas.

Cell Death↗
PubMed2001

Outcome after mild-to-moderate blunt head injury: effects of focal lesions and diffuse axonal injury.

PRIMARY OBJECTIVE: A comparison of the effects of focal and diffuse axonal injury in mild-to-moderate traumatic brain injury (TBI). RESEARCH DESIGN: In a prospective longitudinal study of 138 consecutive patients suffering from TBI who were admitted to the Magdeburg University Hospital, 60 could be assessed neuropsychologically 8--31 days after trauma and 18--45 weeks later. METHODS AND PROCEDURES: GCS, CT-analysis, comprehensive neuropsychological assessment. MAIN RESULTS: The initial GCS-score was significantly correlated with outcome impairments of semantic fluency and memory in the Wechsler Similarities and in two clinical scales (Neurobehavioural Rating Scale, Frontal Lobe Score). The presence of CT-signs of DAI corresponded with deficits in tasks of response selection and suppression, the presence of focal contusions with results in the clinical scales, reaching significance for behavioural deficits with frontal contusions. Improvements between first and second assessments were pronounced in patients with signs of DAI. CONCLUSIONS: The data indicate that traumatic DAI results in mainly transient neuropsychological deficits. Focal frontal contusions result in more relevant deficits at outcome that affect behaviour and, thus, impair rehabilitation prognosis. It is concluded that even in clinically 'mild' TBI, prognosis and rehabilitation requirements should be established by early imaging and post-acute neuropsychological assessment.

Adolescent↗
PubMed2000

Coping with illness after brain diseases--a comparison between patients with malignant brain tumors, stroke, Parkinson's disease and traumatic brain injury.

PURPOSE: This study investigates coping styles in patients suffering from different brain disorders (malignant brain tumors, stroke, Parkinson's disease and traumatic brain injury). METHOD: In a combined analysis of four prospective studies we investigated 21 patients with malignant glioma at the end radiochemotherapy, 30 patients one year after ischemic stroke, 54 patients suffering from various stages of Parkinson's disease, and 58 patients 6 to 8.5 months after traumatic brain injury. The assessment of coping with illness was based on the Freiburg Questionnaire on Coping with illness. RESULTS: With few exceptions, coping styles did not differ across the various brain pathologies. Differences occurred with respect to 'active, problem-oriented coping' (decreased in stroke patients), and coping by search for religious relief or quest for sense (increased in patients with Parkinson's disease). CONCLUSION: Differences in coping styles could be mainly related to age and social factors. Individual coping strategies seem only to be little related to the type of brain pathology.

Acute Disease↗
PubMed2001

The neuropsychology of blunt head injury in the early postacute stage: effects of focal lesions and diffuse axonal injury.

This investigation evaluated the neuropsychological symptoms in the early posttraumatic period following blunt head injury and their correlation to routine imaging data in a consecutive series of TBI patients (Magdeburg Neurotrauma Databank). Of 135 consecutive patients, 68 could be assessed neuropsychologically 8-21 days after trauma. In 61 patients, routine clinical CT data were sufficient for neuroradiological analysis focusing on the presence or absence of CT signs of diffuse axonal injury (DAI) or focal traumatic injury. In these patients, the initial GCS score was significantly correlated with the presence of DAI but not with focal pathology. The presence of DAI was correlated with behavioral and cognitive symptoms of frontal lobe dysfunction, especially in interference tasks (Go/NoGO and Stroop reaction times) and semantic fluency. The presence of local frontal or temporal traumatic lesions was associated with deficits in concept formation, fluency tasks and behavioral symptoms, but not with increased interference. Patients with frontal contusions were impaired in a task of visuomotor planning and performance (Block design). Our data indicate that both traumatic DAI and focal lesions result in frontal lobe symptoms. We conclude that, even in clinically "mild" TBI, brain imaging should be used to identify patients with substantial brain damage. These should be assessed neuropsychologically for possible posttraumatic cognitive or behavioral impairment. In consideration of its easy accessibility, the refined use of the CT is considered a promising and valid tool for patient stratification. The application of MRI and biochemical markers may further improve prognostic predictions.

Adolescent↗
PubMed2006

Mental chronometry of target detection: human thalamus leads cortex.

Attentive monitoring of environmental stimuli is most fundamental for rapid target detection. The aim of this study was to assess the timing of thalamic versus cortical processes involved in this cognitive operation. To this end, simultaneous depth and scalp EEG was recorded in eight patients with essential tremor, undergoing thalamic deep brain stimulation (DBS), when the DBS electrodes could be accessed via their temporarily externalized leads. The patients performed an oddball task consisting of 300 presentations of one frequent and two rare visual cues, appearing in randomized order. One of the rare cues was defined as a target, the occurrences of which had to be indicated by a button press (motor condition) or silently counted (non-motor condition). At the scalp and the thalamus, event-related potentials (ERP) were largest upon target presentation, with peak latencies in the time domain of classical P300 responses. Remarkably, target-specific thalamic ERP emerged significantly prior to scalp P300. Furthermore, whereas scalp ERP had a higher amplitude upon rare than upon frequent non-target signals, thalamic ERP were independent of stimulus probability. This pattern was identified during motor and non-motor task execution. We conclude that the human thalamus specifically supports the early recognition of target events and can widely distribute this label through its divergent cortical projections.

Adult↗
PubMed2001

Somatotopic organization of human secondary somatosensory cortex.

This fMRI study investigated the human somatosensory system, especially the secondary somatosensory cortex (SII), with respect to its potential somatotopic organization. Eight subjects received electrical stimulation on their right second finger, fifth finger and hallux. Within SII, the typical finding for both fingers was a representation site within the contralateral parietal operculum roughly halfway between the lip of the lateral sulcus and its fundus, whereas the representation site of the hallux was found more medially to this position at the fundus of the lateral sulcus, near the posterior pole of the insula. Somatotopy in SII seems to be less fine-grained than in primary somatosensory cortex (SI), as, in contrast to SI, no separate representations of the two fingers in SII were observed. A similar somatotopic representation pattern between fingers and the hallux was also observed within ipsilateral SII, indicating somatotopy of contra- as well as ipsilateral SII using unilateral stimulation. Further areas exhibiting activation were found in the superior and inferior parietal lobule, in the supplementary and cingulate motor area, and in the insula.

Adult↗
PubMed1998

fMRI assessment of somatotopy in human Brodmann area 3b by electrical finger stimulation.

Functional magnetic resonance imaging (fMRI) is capable of detecting focal brain activation induced by electrical stimulation of single fingers in human subjects. In eight subjects somatotopic arrangement of the second and fifth finger was found in Brodmann area 3b of the primary somatosensory cortex. In four subjects the representation area of the second finger was located lateral and inferior to the fifth finger; in one subject the somatotopy was reversed. In three subjects representation areas of the two fingers in Brodmann area 3b were found overlapping. Additional activated areas were found on the crown of ipsilateral and contralateral postcentral gyrus (Brodmann areas 1 and 2) and posterior parietal cortex.

Adult↗
PubMed1999

Multiple generators of 600 Hz wavelets in human SEP unmasked by varying stimulus rates.

Human scalp-derived somatosensory evoked potentials contain a high-frequency wavelet burst, presumably reflecting repetitive synchronized population spikes. Here, the burst refractory behavior was characterized using median nerve electrostimulation with 18 frequencies (0.5-25Hz) for comparison with cellular burst characteristics. Above 10 Hz only a brief high-frequency (700 Hz) burst component remained discernible, which gradually decreased; possible generators comprise cells capable of generating spike bursts of extraordinarily high frequency, such as pyramidal 'chattering cells', cortical fast spiking inhibitory interneurons and some thalamocortical relay cells. At stimulation frequencies <4 Hz an additional late burst component appeared with only 494 Hz intraburst frequency. Comparably long refractory periods and low intraburst frequencies have been described for bursting cells driven by low-threshold calcium currents.

Action Potentials↗
PubMed1999

Spatiotemporal characteristics of human intrathalamic high-frequency (>400Hz) SEP components.

Somatosensory evoked potentials (SEP) were recorded in 11 awake patients from intrathalamic electrodes implanted for tremor treatment. A brief (7ms) polyphasic SEP burst (mean frequency > 1000 Hz, with occasional drops to 600 Hz) was found to be superimposed onto the primary thalamic low-frequency response at 16 ms (tP16) and preceeded a scalp-derived 600 Hz burst by 4 ms. Thalamic burst and tP16 generators had a close intrathalamic co-localization. The thalamic burst strength varied more than and independently from tP16. High-frequency thalamic SEP bursts probably reflect a superposition of slightly asynchronously triggered population spikes, generated e.g. by bursting thalamocortical relay cells. The thalamic burst amplitude fluctuations independent from low-frequency responses suggest a peculiar role for thalamic burst coding in awake subjects.

Adult↗
PubMed2000

Double-pulse stimulation dissociates intrathalamic and cortical high-frequency (>400Hz) SEP components in man.

Human somatosensory evoked potentials (SEP) contain high-frequency (600 Hz) wavelet bursts possibly reflecting repetitive population spikes in thalamocortical axons and/or postsynaptic responses. To dissociate thalamic and cortical burst components the recovery of intrathalamic SEP (derived from electrodes implanted for movement disorder therapy in seven patients) was compared with scalp SEP in six age-matched Parkinsonian patients and six healthy younger subjects. Upon electric median nerve double-pulse stimulation conditioned scalp bursts were found attenuated in both groups, more for 10ms than 20ms interstimulus intervals; moreover, intraburst frequencies decreased from 690Hz to 590Hz. By contrast, intrathalamic burst amplitudes and frequencies (around 1 kHz) remained largely stable. These dissociations indicate functionally distinct generator mechanisms for scalp and intrathalamic high-frequency SEP bursts.

Action Potentials↗
PubMed2000

Propofol narcosis dissociates human intrathalamic and cortical high-frequency (> 400 hz) SEP components.

Human somatosensory evoked potentials (SEP) contain a brief burst of high-frequency wavelets (>400 Hz) presumably reflecting rapidly repeated population spikes of as-yet undetermined origin. To study state-dependent response changes, SEP after electric median nerve stimulation were recorded in six Parkinson's disease patients perioperatively from intrathalamic electrode implants, and in five non-implanted patients from scalp electrodes, before and under propofol narcosis. In all intrathalamic recordings burst amplitude and intraburst frequency (approximately 950 Hz) proved to be almost stable under propofol administration. In strong contrast, the scalp burst (640 Hz) was significantly slowed (480 Hz) under propofol narcosis, and its amplitude reduced to 28% of the pre-propofol baseline. Low-frequency SEP components which underly the burst at thalamic (P16) and cortical level (N20) did not change significantly. This dissociation of bursts indicates neuronal generators showing different sensitivities to propofol narcosis, with a robust thalamic response and a state-dependent cortical contribution, possibly from pyramidal chattering cells and/or inhibitory interneurons.

Action Potentials↗
PubMed2001

Independent short-term variability of spike-like (600 Hz) and postsynaptic (N20) cerebral SEP components.

Human scalp-derived somatosensory evoked potentials (SEP) elicited by median nerve stimulation contain an early (20 ms latency) high-frequency (600 Hz) wavelet burst which is supposed to reflect non-invasively the timing of rapidly repeating population spikes in thalamocortical afferences and/or the receiving neocortical cell populations. This burst is superimposed onto the slower (< or = 100 Hz) primary cortical response (N20) representing intracortically generated postsynaptic events. The present study addressed the temporal dynamics and correlation of these response components in awake human subjects and found that at a 3 min time scale the burst response was significantly more variable than the concomitant N20, and that the burst and N20 varied independently of each other. Thus, wavelet burst and N20 represent parallel and partly independent steps in sensory processing at cortical input stages in awake human subjects. We propose that the N20 represents a stable somatosensory input whereas the more fluctuating high-frequency burst could index variable modes of processing, such as a floating focus of attention.

Adolescent↗