8 research outputs found
Independent Component Analysis for Source Localization of EEG Sleep Spindle Components
Sleep spindles are bursts of sleep electroencephalogram (EEG) quasirhythmic activity within the frequency band of 11–16 Hz, characterized by progressively increasing, then gradually decreasing amplitude. The purpose of the present study was to process sleep spindles with Independent Component Analysis (ICA) in order to investigate the possibility of extracting, through visual analysis of the spindle EEG and visual selection of Independent Components (ICs), spindle “components” (SCs) corresponding to separate EEG activity patterns during a spindle, and to investigate the intracranial current sources underlying these SCs. Current source analysis using Low-Resolution Brain Electromagnetic Tomography (LORETA) was applied to the original and the ICA-reconstructed EEGs. Results indicated that SCs can be extracted by reconstructing the EEG through back-projection of separate groups of ICs, based on a temporal and spectral analysis of ICs. The intracranial current sources related to the SCs were found to be spatially stable during the time evolution of the sleep spindles
Automated Sleep Spindle Detection System using Period-Amplitude Analysis
Sleep spindles are rhythmic transient waveforms present in the
electroencephalogram (EEG) of non-rapid eye movement (NREM) sleep. In
the present study a period-amplitude analysis method was applied for the
automated detection of sleep spindles in all-night sleep EEG recordings
of young healthy subjects. The method relies on the characterization of
individual half-waves of the EEG data, by estimating electrographic
parameters such as amplitude and duration and by assigning a grade to
each half-wave depending on where it lies in the amplitude-frequency
plane. The grading is followed by the detection system, checking
consecutive half-wave characteristics and implementing a set of rules
for determining the start and the end of spindle bursts and for
retaining or rejecting sleep spindle indications provided during the
various stages of the detection system. The sensitivity and false
positive rate across subjects was 78.9% and 10.9%, respectively,
providing indication that the method could be successfully applied to
larger sets of healthy subjects of various age groups, as well as to
patient populations
Melatonin secretion after head injury: A pilot study
Primary objective: To investigate the circadian rhythm of serum
melatonin in patients with traumatic brain injury (TBI) during Intensive
Care Unit (ICU) stay and its relationship with core body temperature
fluctuations and measures of severity of their condition.
Methods and procedures: The pilot study was conducted in the ICU of a
general hospital in Athens, Greece. Blood melatonin was determined in
eight patients consecutively admitted at the ICU following severe head
injury, eight times per day during the first and second day following
admission. Core body temperature was recorded at hourly intervals.
Patients were also assessed with the Glasgow Coma Score (GCS) and the
APACHE II score.
Results: Melatonin concentrations were lower than the normally reported
values. Mean night-time melatonin levels were higher than mean daytime
levels both on the first and second days, although not statistically
significant. Diurnal variation of melatonin was associated with the GCS.
Thus, patients with low GCS (n=4) did not exhibit a consistent diurnal
variation of melatonin, whereas those with high GCS (n = 4) retained the
normally expected fluctuations.
Conclusions: ICU-treated TBI patients exhibit reduced melatonin levels
and a circadian secretion profile which is related to the severity of
the injury. Patients with more severe head trauma exhibit a clearly
disrupted pattern of melatonin secretion, whereas those with less severe
trauma preserve a relatively intact diurnal rhythm. Furthermore, the
diurnal secretion pattern of melatonin appeared to be dissociated from
the circadian rhythm of core body temperature. These preliminary
findings may have implications for the management of TBI patients
Sleep EEG and Spindle Characteristics After Combination Treatment With Clozapine in Drug-Resistant Schizophrenia: A Pilot Study
Purpose: Clozapine is an atypical neuroleptic agent, effective in
treating drug-resistant schizophrenia. The aim of this work was to
investigate overall sleep architecture and sleep spindle morphology
characteristics, before and after combination treatment with clozapine,
in patients with drug-resistant schizophrenia who underwent
polysomnography.
Methods: Standard polysomnographic techniques were used. To quantify the
sleep spindle morphology, a modeling technique was used that quantifies
time-varying patterns in both the spindle envelope and the intraspindle
frequency.
Results: After combination treatment with clozapine, the patients showed
clinical improvement. In addition, their overall sleep architecture and,
more importantly, parameters that quantify the time-varying sleep
spindle morphology were affected. Specifically, the results showed
increased stage 2 sleep, reduced slow-wave sleep, increased rapid eye
movement sleep, increased total sleep time, decreased wake time after
sleep onset, as well as effects on spindle amplitude and intraspindle
frequency parameters. However, the above changes in overall sleep
architecture were statistically non-significant trends.
Conclusions: The findings concerning statistically significant effects
on spindle amplitude and intraspindle frequency parameters may imply
changes in cortical sleep EEG generation mechanisms, as well as changes
in thalamic pacing mechanisms or in thalamo-cortical network dynamics
involved in sleep EEG generation, as a result of combination treatment
with clozapine. Significance: Sleep spindle parameters may serve as
metrics for the eventual development of effective EEG biomarkers to
investigate treatment effects and pathophysiological mechanisms in
schizophrenia
Dynamics of regional brain activity in epilepsy: a cross-disciplinary study on both intracranial and scalp-recorded epileptic seizures
Objective. Recent cross-disciplinary literature suggests a dynamical
analogy between earthquakes and epileptic seizures. This study extends
the focus of inquiry for the applicability of models for earthquake
dynamics to examine both scalp-recorded and intracranial
electroencephalogram recordings related to epileptic seizures. Approach.
First, we provide an updated definition of the electric event in terms
of magnitude and we focus on the applicability of (i) a model for
earthquake dynamics, rooted in a nonextensive Tsallis framework, (ii)
the traditional Gutenberg and Richter law and (iii) an alternative
method for the magnitude-frequency relation for earthquakes. Second, we
apply spatiotemporal analysis in terms of nonextensive statistical
physics and we further examine the behavior of the parameters included
in the nonextensive formula for both types of electroencephalogram
recordings under study. Main results. We confirm the previously observed
power-law distribution, showing that the nonextensive formula can
adequately describe the sequences of electric events included in both
types of electroencephalogram recordings. We also show the intermittent
behavior of the epileptic seizure cycle which is analogous to the
earthquake cycles and we provide evidence of self-affinity of the
regional electroencephalogram epileptic seizure activity. Significance.
This study may provide a framework for the analysis and interpretation
of epileptic brain activity and other biological phenomena with similar
underlying dynamical mechanisms
Differences in EEG Delta Frequency Characteristics and Patterns in Slow-Wave Sleep Between Dementia Patients and Controls: A Pilot Study
Purpose: To evaluate the modifications of EEG activity during slow-wave
sleep in patients with dementia compared with healthy elderly subjects,
using spectral analysis and period-amplitude analysis.
Methods: Five patients with dementia and 5 elderly control subjects
underwent night polysomnographic recordings. For each of the first three
nonrapid eye movement-rapid eye movement sleep cycles, a well-defined
slow-wave sleep portion was chosen. The delta frequency band (0.4-3.6
Hz) in these portions was analyzed with both spectral analysis and
period-amplitude analysis.
Results: Spectral analysis showed an increase in the delta band power in
the dementia group, with a decrease across the night observed only in
the control group. For the dementia group, period-amplitude analysis
showed a decrease in well-defined delta waves of frequency lower than
1.6 Hz and an increase in such waves of frequency higher than 2 Hz, in
incidence and amplitude.
Conclusions: Our study showed (1) a loss of the dynamics of delta band
power across the night sleep, in dementia, and (2) a different
distribution of delta waves during slow-wave sleep in dementia compared
with control subjects. This kind of computer-based analysis can
highlight the presence of a pathologic delta activity during slow-wave
sleep in dementia and may support the hypothesis of a dynamic
interaction between sleep alteration and cognitive decline