43 research outputs found
Topography of Cortical Activation Differs for Fundamental and Harmonic Frequencies of the Steady-State Visual-Evoked Responses. An EEG and PET H15 2 O Study
In humans, visual flicker stimuli of graded frequency (2--90 Hz) elicit
an electroencephalographic (EEG) steady-state visual-evoked response
(SSVER) with the same fundamental frequency as the stimulus
and, in addition, a series of harmonic responses. The fundamental
component of the SSVER is generated by increased synaptic activity
in primary visual cortex (V1). We set out to determine the cortical
origin of the harmonic responses in humans. For this purpose, we
recorded the SSVERs at 5 different frequencies (5, 10, 15, 25, and 40
Hz) and measured regional cerebral blood flow (rCBF) with positron
emission tomography-H15
2 O at rest and during visual stimulation at
the same frequencies. The rCBF contrast weighted by the amplitude
of the SSVERs first harmonics showed activation of a swath of cortex
perpendicular to V1, including mostly the inferior half of the parietooccipital
sulcus. This area overlapped minimally with the primary
visual cortex activated by the fundamental frequency. A different
method, estimating EEG cortical source current density with lowresolution
brain electromagnetic tomography, gave the same results.
Our finding suggests that the inferior portion of the banks of the
parieto-occipital sulci contains association visual cortex involved in
the procparieto-occipital sulcus
Alpha and beta oscillatory activity during a sequence of two movements
OBJECTIVE:
We studied movement-related electroencephalographic oscillatory changes in the alpha and beta range during a sequence of two movements in 7 healthy volunteers, in order to investigate the relationship between these changes and each component in the sequence.
METHODS:
The sequence consisted of a wrist active extension-passive flexion followed by a first and second finger pincer. A total of 10.5 s sweeps were recorded using the level of surface electromyographic (EMG) activity in wrist extensors as trigger, including a 7.5 s pre-stimulus. The sweeps were also realigned manually offline using as trigger the end of the first EMG burst, or the beginning of the second movement. An index of the changes in non-phase-locked energy in the 7-37 Hz range was obtained by averaging single-sweep time-frequency transforms.
RESULTS:
The duration of each of the movements in the sequence and the relationship between them were compatible with the use of two different motor programmes in the sequence. In the beta band, a decrease in energy (event-related desynchronisation, ERD) began 1.5 s before the onset of the first movement, and was sustained until the end of the second movement. No energy increases were observed until the end of the second movement. In the alpha band, the ERD began 0.5 seconds before the first movement and was sustained throughout the recording.
CONCLUSION:
These findings suggest that the beta-event-related synchronisation is related to the end of the whole motor process, and not to the end of each motor programme
Paresia poscrÃtica durante estudios de monitorización de vÃdeo-EEG
To know the frequency of Todd s paralysis during the video EEG
monitoring studies, to investigate in its pathophysiology, and to confirm its
value to localise the epileptic focus. PATIENTS AND METHODS: We reviewed 114
monitoring studies, in 102 patients. RESULTS: Sixty patients had epileptic
seizures. An obvious paresis was noted in four seizures of two patients (3 and 1,
respectively). Both patients had frontal epilepsy. During the paralysis, in the
first patient the EEG showed ictal discharges on the contralateral centrotemporal
area. In the second patient, the EEG demonstrated slow waves in the contralateral
frontal region. The ictal onset was contralateral to the paresis in all cases. No
patient with pseudoseizures had paralysis. CONCLUSIONS: Postconvulsive paralysis
are not frequent in video EEG monitoring studies. However, if present it points
out to a contralateral seizure onset. In our series it happened in patients with
frontal seizures. The EEG may help to clarify if it correspond to a true
postictal phenomenon or to a ictal paralysis
Changes in the heart rate variability in patients with obstructive sleep apnea and its response to acute CPAP treatment
Obstructive Sleep Apnea (OSA) is a major risk factor for
cardiovascular disease. The goal of this study was to demonstrate whether the use
of CPAP produces significant changes in the heart rate or in the heart rate
variability of patients with OSA in the first night of treatment and whether
gender and obesity play a role in these differences. METHODS: Single-center
transversal study including patients with severe OSA corrected with CPAP. Only
patients with total correction after CPAP were included. Patients underwent two
sleep studies on consecutive nights: the first night a basal study, and the
second with CPAP. We also analyzed the heart rate changes and their relationship
with CPAP treatment, sleep stages, sex and body mass index. Twenty-minute
segments of the ECG were selected from the sleep periods of REM, no-REM and
awake. Heart rate (HR) and heart rate variability (HRV) were studied by comparing
the R-R interval in the different conditions. We also compared samples from the
basal study and CPAP nights. RESULTS: 39 patients (15 females, 24 males) were
studied. The mean age was 50.67 years old, the mean AHI was 48.54, and mean body
mass index was 33.41 kg/m(2) (31.83 males, 35.95 females). Our results showed
that HRV (SDNN) decreased after the use of CPAP during the first night of
treatment, especially in non-REM sleep. Gender and obesity did not have any
influence on our results. CONCLUSIONS: These findings support that cardiac
variability improves as an acute effect, independently of gender or weight, in
the first night of CPAP use in severe OSA patients, supporting the idea of
continuous use and emphasizing that noncompliance of CPAP treatment should be
avoided even if it is just once
Slow oscillatory activity and levodopa-induced dyskinesias in Parkinson’s disease
The pathophysiology of levodopa-induced dyskinesias (LID) in Parkinson’s disease is not well understood.
We have recorded local field potentials (LFP) from macroelectrodes implanted in the subthalamic nucleus
(STN) of 14 patients with Parkinson’s disease following surgical treatment with deep brain stimulation. Patients
were studied in the ‘Off’ medication state and in the ‘On’ motor state after administration of levodopa–
carbidopa (po) or apomorphine (sc) that elicited dyskinesias in 11 patients. The logarithm of the power
spectrum of the LFP in selected frequency bands (4–10, 11–30 and 60–80 Hz) was compared between the
‘Off’ and ‘On’ medication states. A peak in the 11–30 Hz band was recorded in the ‘Off’ medication state
and reduced by 45.2% (P < 0.001) in the ‘On’ state. The ‘On’ was also associated with an increment of 77. 6%
(P < 0.001) in the 4–10 Hz band in all patients who showed dyskinesias and of 17.8% (P < 0.001) in the 60–80 Hz
band in the majority of patients. When dyskinesias were only present in one limb (n = 2), the 4–10 Hz peak was
only recorded in the contralateralSTN. These findings suggest that the 4–10 Hz oscillation is associated with the
expression of LID in Parkinson’s disease
Involvement of the subthalamic nucleus in impulse control disorders associated with Parkinson’s disease
Behavioural abnormalities such as impulse control disorders may develop when patients with Parkinson’s disease receive
dopaminergic therapy, although they can be controlled by deep brain stimulation of the subthalamic nucleus. We have recorded
local field potentials in the subthalamic nucleus of 28 patients with surgically implanted subthalamic electrodes. According to
the predominant clinical features of each patient, their Parkinson’s disease was associated with impulse control disorders
(n = 10), dyskinesias (n = 9) or no dopaminergic mediated motor or behavioural complications (n = 9). Recordings were obtained
during the OFF and ON dopaminergic states and the power spectrum of the subthalamic activity as well as the subthalamocortical
coherence were analysed using Fourier transform-based techniques. The position of each electrode contact was determined
in the postoperative magnetic resonance image to define the topography of the oscillatory activity recorded in each
patient. In the OFF state, the three groups of patients had similar oscillatory activity. By contrast, in the ON state, the patients
with impulse control disorders displayed theta-alpha (4–10 Hz) activity (mean peak: 6.71 Hz) that was generated 2–8mm below
the intercommissural line. Similarly, the patients with dyskinesia showed theta-alpha activity that peaked at a higher frequency
(mean: 8.38 Hz) and was generated 0–2mm below the intercommissural line. No such activity was detected in patients that
displayed no dopaminergic side effects. Cortico-subthalamic coherence was more frequent in the impulsive patients in the
4–7.5 Hz range in scalp electrodes placed on the frontal regions anterior to the primary motor cortex, while in patients with
dyskinesia it was in the 7.5–10 Hz range in the leads overlying the primary motor and supplementary motor area. Thus,
dopaminergic side effects in Parkinson’s disease are associated with oscillatory activity in the theta-alpha band, but at different
frequencies and with different topography for the motor (dyskinesias) and behavioural (abnormal impulsivity) manifestations.
These findings suggest that the activity recorded in parkinsonian patients with impulse control disorders stems from the
associative-limbic area (ventral subthalamic area), which is coherent with premotor frontal cortical activity. Conversely, in
patients with L-dopa-induced dyskinesias such activity is recorded in the motor area (dorsal subthalamic area) and it is coherent
with cortical motor activity. Consequently, the subthalamic nucleus appears to be implicated in the motor and behavioural
complications associated with dopaminergic drugs in Parkinson’s disease, specifically engaging different anatomo-functional
territories
Effect of sugammadex on processed EEG parameters in patients undergoing robot-assisted radical prostatectomy
Background: Sugammadex has been associated with increases in the bispectral index (BIS). We evaluated the effects of
sugammadex administration on quantitative electroencephalographic (EEG) and electromyographic (EMG) measures.
Methods: We performed a prospective observational study of adult male patients undergoing robot-assisted radical
prostatectomy. All patients received a sevoflurane-based general anaesthetic and a continuous infusion of rocuronium,
which was reversed with 2 mg kg1 of sugammadex i.v. BIS, EEG, and EMG measures were captured with the BIS Vistaâ„¢
monitor.
Results: Twenty-five patients were included in this study. Compared with baseline, BIS increased at 4e6 min (b coefficient: 3.63; 95% confidence interval [CI]: 2.22e5.04; P<0.001), spectral edge frequency 95 (SEF95) increased at 2e4 min (b
coefficient: 0.29; 95% CI: 0.05e0.52; P¼0.016) and 4e6 min (b coefficient: 0.71; 95% CI: 0.47e0.94; P<0.001), and EMG
increased at 4e6 min (b coefficient: 1.91; 95% CI: 1.00e2.81; P<0.001) after sugammadex administration. Compared with
baseline, increased beta power was observed at 2e4 min (b coefficient: 93; 95% CI: 1e185; P¼0.046) and 4e6 min (b coefficient: 208; 95% CI: 116e300; P<0.001), and decreased delta power was observed at 4e6 min (b coefficient: 526.72; 95%
CI: 778 to 276; P<0.001) after sugammadex administration. Neither SEF95 nor frequency band data analysis adjusted
for EMG showed substantial differences. None of the patients showed clinical signs of awakening.
Conclusions: After neuromuscular block reversal with 2 mg kg1 sugammadex, BIS, SEF95, EMG, and beta power showed
small but statistically significant increases over time, while delta power decreased
Delta-mediated cross-frequency coupling organizes oscillatory activity across the rat cortico-basal ganglia network
The brain's ability to integrate different behavioral and cognitive processes relies on its capacity to generate neural oscillations in a cooperative and coordinated manner. Cross-frequency coupling (CFC) has recently been proposed as one of the mechanisms involved in organizing brain activity. Here we investigated the phase-to-amplitude CFC (PA-CFC) patterns of the oscillatory activity in the cortico-basal ganglia network of healthy, freely moving rats. Within-structure analysis detected consistent PA-CFC patterns in the four regions analyzed, with the phase of delta waves modulating the amplitude of activity in the gamma (low-gamma ~50 Hz; high-gamma ~80 Hz) and high frequency ranges (high frequency oscillations HFO, ~150 Hz). Between-structure analysis revealed that the phase of delta waves parses the occurrence of transient episodes of coherence in the gamma and high frequency bands across the entire network, providing temporal windows of coherence between different structures. Significantly, this specific spatio-temporal organization was affected by the action of dopaminergic drugs. Taken together, our findings suggest that delta-mediated PA-CFC plays a key role in the organization of local and distant activities in the rat cortico-basal ganglia network by fine-tuning the timing of synchronization events across different structures. KEYWORDS:
cortico-basal ganglia network; cross-frequency coupling; dopaminergic system; local field potentials; nested interactions; nested oscillations; oscillatory activit
VÃdeo-electroencefalografÃa: una necesidad
El vÃdeo-EEG es una herramienta diagnóstica habitual. Los avances técnicos de la última década la han
simplificado de tal modo que con poco más de un ordenador y una cámara de vÃdeo pueden conseguirse registros de calidad. Se requiere personal preparado para
su ejecución e interpretación. Es muy útil para el diagnóstico de episodios paroxÃsticos, para la clasificación
y caracterización de crisis epilépticas y para la cuantificación de crisis o grafoelementos epileptiformes. Dada
la importancia de un diagnóstico exacto, certero, ante
un episodio paroxÃstico, no cabe duda de que esta herramienta debe ser cada vez más asequible para evitar
el mal trato a muchos enfermos neurológicos. A pesar
del paso de los años, un 20-30% de pacientes diagnosticados de epilepsia no son realmente epilépticos, lo cual
sigue siendo excesivo e inaceptable.The video-EEG is a common diagnostic tool
nowadays. The technical achievements of the last decade have brought a simplification of the equipment
required to obtain good quality recordings, with little
more than a computer and a video camera being necessary. However, the medical and technical staff must
be well trained to execute and interpret the study. It
is very useful in the diagnosis of paroxysmal events,
for the classification and characterization of epileptic
seizures and to quantify epileptiform discharges. Due
to the importance of a correct diagnosis to avoid mistreating many neurological patients, this tool should be
accessible to clinicians. In spite of the advances of recent years, 20-30% of patients diagnosed with epilepsy
are not really epileptic, a fact that it is excessive and
unacceptabl
Effects of dexmedetomidine on subthalamic local field potentials in parkinson's disease
Background: Dexmedetomidine is frequently used for sedation during deep brain stimulator implantation in patients with Parkinson's disease, but its effect on subthalamic nucleus activity is not well known. The aim of this study was to quantify the effect of increasing doses of dexmedetomidine in this population.
Methods: Controlled clinical trial assessing changes in subthalamic activity with increasing doses of dexmedetomidine (from 0.2 to 0.6 μg kg-1 h-1) in a non-operating theatre setting. We recorded local field potentials in 12 patients with Parkinson's disease with bilateral deep brain stimulators (24 nuclei) and compared basal activity in the nuclei of each patient and activity recorded with different doses. Plasma levels of dexmedetomidine were obtained and correlated with the dose administered.
Results: With dexmedetomidine infusion, patients became clinically sedated, and at higher doses (0.5-0.6 μg kg-1 h-1) a significant decrease in the characteristic Parkinsonian subthalamic activity was observed (P<0.05 in beta activity). All subjects awoke to external stimulus over a median of 1 (range: 0-9) min, showing full restoration of subthalamic activity. Dexmedetomidine dose administered and plasma levels showed a positive correlation (repeated measures correlation coefficient=0.504; P<0.001).
Conclusions: Patients needing some degree of sedation throughout subthalamic deep brain stimulator implantation for Parkinson's disease can probably receive dexmedetomidine up to 0.6 μg kg-1 h-1 without significant alteration of their characteristic subthalamic activity. If patients achieve a 'sedated' state, subthalamic activity decreases, but they can be easily awakened with a non-pharmacological external stimulus and recover baseline subthalamic activity patterns in less than 10 min