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Gabriel Curio

Publications and source records attributed to Gabriel Curio.

29 records · Page 2Linked to original sources
PubMed2003

EEG oscillations at 600 Hz are macroscopic markers for cortical spike bursts.

The human electroencephalogram (EEG) is generated predominantly by synchronised cortical excitatory postsynaptic potentials oscillating at frequencies <100 Hz. Unusually, EEG responses to electrical nerve stimulation contain brief bursts of high-frequency (600 Hz) wavelets. Here we show, in awake monkeys, that a subset of primary somatosensory cortex single units consistently fires both bursts and single spikes phase-locked to EEG wavelets. Spike bursts were also evoked by tactile stimuli, proving that this is a natural response mode. EEG wavelets at 600 Hz may therefore permit non-invasive assessment of population spike timing in human cortex.

Animals↗
PubMed2003

The eloquence of silent cortex: analysis of afferent input to deafferented cortex in arm amputees.

Cortical reorganisation after limb amputation includes topographic displacements of body representation areas and changes of areal extent. Remarkably, truncated nerves, which had innervated amputated limb parts and remained in the residual limbs, can retain access to the deafferented somatosensory cortex. Using somatosensory evoked potentials (SEP) we characterized afferences from electrically stimulated truncated nerves to the brachial plexus and cortex in 12 arm amputees. While peripheral responses were highly variable, thalamocortical input to S-1, as reflected by the primary cortical SEP component, was present in 11 of 12 patients. Despite long-term deafferentation, macroscopic phenomena of inhibition/refractoriness, as assessed by stimulus rate variations, appeared to be changed only marginally. Thus, deafferented cortex remains responsive when given artificial phantom input and could provide a neuronal substrate for spontaneous phantom limb sensations, including phantom pain.

Adult↗
PubMed2003

Boosting bit rates and error detection for the classification of fast-paced motor commands based on single-trial EEG analysis.

Brain-computer interfaces (BCIs) involve two coupled adapting systems--the human subject and the computer. In developing our BCI, our goal was to minimize the need for subject training and to impose the major learning load on the computer. To this end, we use behavioral paradigms that exploit single-trial EEG potentials preceding voluntary finger movements. Here, we report recent results on the basic physiology of such premovement event-related potentials (ERP). 1) We predict the laterality of imminent left- versus right-hand finger movements in a natural keyboard typing condition and demonstrate that a single-trial classification based on the lateralized Bereitschaftspotential (BP) achieves good accuracies even at a pace as fast as 2 taps/s. Results for four out of eight subjects reached a peak information transfer rate of more than 15 b/min; the four other subjects reached 6-10 b/min. 2) We detect cerebral error potentials from single false-response trials in a forced-choice task, reflecting the subject's recognition of an erroneous response. Based on a specifically tailored classification procedure that limits the rate of false positives at, e.g., 2%, the algorithm manages to detect 85% of error trials in seven out of eight subjects. Thus, concatenating a primary single-trial BP-paradigm involving finger classification feedback with such secondary error detection could serve as an efficient online confirmation/correction tool for improvement of bit rates in a future BCI setting. As the present variant of the Berlin BCI is designed to achieve fast classifications in normally behaving subjects, it opens a new perspective for assistance of action control in time-critical behavioral contexts; the potential transfer to paralyzed patients will require further study.

Algorithms↗
PubMed2002

Dissociation of human thalamic and cortical SEP gating as revealed by intrathalamic recordings under muscle relaxation.

'Gating' refers to a reduction of cortical somatosensory evoked potentials (SEP) under multiple simultaneous afferent inputs. This study used the opportunity for intrathalamic recordings in patients with movement disorders to clarify to what extent cortical SEP gating is preceded by thalamic gating. Recordings were performed in 10 patients, narcotised by intravenous propofol when receiving implantation of a therapeutic deep brain stimulator system. SEP were elicited by an 8.1-Hz median nerve stimulation at twice motor threshold and were recorded simultaneously from both intrathalamic and scalp electrodes before and after the application of the depolarising muscle blocker succinylcholine which eliminated both the background muscular tone and the repetitive muscle twitches caused by the median nerve stimulation. Peripheral compound action potentials recorded at the upper arm remained unchanged after complete muscle relaxation, proving a continuously effective nerve stimulation. In contrast, the primary cortical SEP component (N20) was significantly increased under succinylcholine (+17%). This cortical release from gating was not paralleled, however, by an increased thalamic response; rather, the primary thalamic response (P16) showed a slight (-9%) but highly significant amplitude reduction. As the recordings were performed in narcotised patients, any potentially variable attentional bias on part of the subjects can be excluded as confounding factor when comparing the two experimental conditions with vs. without reafferent somatosensory inflow. Thus, given the high signal-to-noise ratio of intrathalamically recorded SEP, the present study shows a distinct thalamo-cortical dissociation with the primary somatosensory cortex representing the predominant level exhibiting SEP gating.

Action Potentials↗
PubMed2002

Event-related fMRI of the somatosensory system using electrical finger stimulation.

Cortical signal intensity changes due to brief (1 s) innocuous electrical stimuli applied to the second and fifth finger of the right hand were measured by means of fMRI at 1.5 T. The activation pattern in this event-related fMRI approach closely resembled that obtained in recent block-design studies. Activations were found in contralateral primary (SI) and bilaterally in secondary (SII) somato-sensory cortex as well as in posterior parietal cortex, insula, and supplementary motor area (SMA). In SI, the somatotopic organization of the hand area is demonstrated, more clearly to be seen in area 3b than in area 1 and 2. In conclusion, the feasibility to employ event-related somatosensory stimulation paradigms in fMRI studies is demonstrated.

Adult↗
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↗
PubMed2002

Cardiac artifact subspace identification and elimination in cognitive MEG data using time-delayed decorrelation.

To reduce physiological artifacts in magnetoencephalographic (MEG) and electroencephalographic recordings, a number of methods have been applied in the past such as principal component analysis, signal-space projection, regression using secondary information, and independent component analysis. This method has become popular as it does not have constraints such as orthogonality between artifact and signal or the need for a priori information. Applying the time-delayed decorrelation algorithm to raw data from a visual stimulation MEG experiment, we show that several of the independent components can be attributed to the cardiac artifact. Calculating an average cardiac activity shows that physiologically different excitation states of the heart produce similar field distributions in the MEG sensor system. This is equivalent to differing spectral properties of cardiac field distributions in the raw data. As a consequence, the algorithm combines, e.g., the R peak and the T wave of the cardiac cycle into a single component and the one-to-one assignment of each independent component with a physiological source is not justified in this case. To improve the signal quality of visually evoked fields, the multidimensional cardiac artifact subspace is suppressed from the data. To assess the preservation of the evoked signal after artifact suppression, a geometrical and a temporal measure are introduced. The suppression of cardiac and alpha wave artifacts allows, in our experimental setting, the reduction of the number of epochs to one half while preserving the visually evoked signal.

Algorithms↗
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↗
PubMedDate not supplied

Patterns of disturbed impulse propagation in multiple sclerosis identified by low and high frequency somatosensory evoked potential components.

In human median nerve somatosensory evoked potentials (SSEPs), high frequency (600 Hz) oscillations (HFOs) are superimposed onto the low frequency SSEP component N20. High frequency oscillations are generated both in deep axon segments of thalamo-cortical projection neurons and at the primary somatosensory cortex. The present study aimed to test the hypothesis that HFOs might be more sensitive to temporal dispersion caused by demyelinating lesions in multiple sclerosis (MS) than the N20. The authors recorded HFOs in median nerve SSEPs in 50 patients with definite MS and in 30 healthy controls. Three patterns of SSEP alterations were found: (1) abolished HFOs with either normal (11% of stimulated limbs), or delayed N20 (16% of stimulated limbs); (2) an attenuation of N20 amplitude with preserved HFOs (13%); and (3) a mixture of both patterns (21%). The first pattern--normal N20 with abolished HFOs--indicates that the HFOs are a sensitive marker of slight demyelination. The second pattern is suggestive of a mainly axonal lesion type, while the third pattern points to a combined axonal/demyelinating process or a conduction block. Analysis of HFOs allows identification of slight demyelinating processes in MS patients in whom the N20 SSEP component remains unaffected. The HFOs provide a tool to distinguish different patterns of disturbed impulse propagation.

Adult↗