Human Cerebral Activation during Steady-State Visual-Evoked Responses

Flicker stimuli of variable frequency (2-90 Hz) elicit a steady-state visual-evoked response (SSVER) in the electroencephalogram (EEG) with the same frequency as the stimulus. In humans, the amplitude of this response peaks at approximately 15 Hz, decreasing at higher stimulation frequencies. It was not known whether this peak response corresponds to increased synaptic activity in the visual cortex or to other mechanisms [for instance, the temporal coherence (phase summation) of evoked responses]. We studied the SSVER in 16 normal volunteers by means of visual stimulation at 14 different frequencies (from 5 to 60 Hz) while recording the EEG. In nine subjects of the group, we measured regional cerebral blood flow (rCBF) with positron emission tomography (PET)-H2(15)O at rest and during visual stimulation at five different frequencies: 5, 10, 15, 25, and 40 Hz. We confirmed that the amplitude of the SSVER in occipital regions peaks at 15 Hz stimulation. Applying to the PET rCBF data a contrast weighted by the amplitude of the SSVER, we determined that the primary visual cortex rCBF follows an activation pattern similar to the SSVER. This finding suggests that the amplitude of the SSVER corresponds to increased synaptic activity, specifically in Brodmann's area 17. Additionally, this study showed that visual stimulation at 40 Hz causes selective activation of the macular region of the visual cortex, and that a region in the dorsal aspect of the Crus I lobule of the left cerebellar hemisphere is activated during repetitive visual stimulation

Resultados de los potenciales evocados miogénicos vestibulares en el vértigo posicional paroxístico benigno

Objective: Benign paroxysmal positional vertigo (BPPV) seems to occur because of otoconia migration into the semicircular canals or their adherence to the cupula. Although the origin of these otoconia lies in the macula of the utricle, vestibular evoked myogenic potentials (VEMPs) can be used assess saccular function. The aim of this study is to assess the saccular function in patients diagnosed with BPPV. Patients and method: Nineteen patients diagnosed with BPPV of the posterior semicircular canal were included in this study. Their auditory function and their caloric, rotatory chair, and VEMP responses were tested. Ipsilateral and contralateral VEMP thresholds, ipsilateral and contralateral p13 and n23 latencies at 100 dB, inter-peak amplitude and the interaural amplitude difference were determined. Results: We found a lack of VEMP response in 52 % of the ears with BPPV. When adjusted for bilateral absence, VEMP response was absent in 20.3 % of ears. Conclusions: Some patients with idiopathic BPPV show a degree of saccular dysfunction

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

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

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 poscrítica durante estudios de monitorización de vídeo-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

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

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

Vídeo-electroencefalografía: una necesidad

El vídeo-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 vídeo pueden conseguirse registros de calidad. Se requiere personal preparado para su ejecución e interpretación. Es muy útil para el diagnóstico de episodios paroxísticos, 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 paroxístico, 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

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