Changes in neocortical function in response to the direct action of optical radiation

The action of optical radiation on neocortical bioelectrical activity and on a penicillin-induced epileptic focus was investigated. The direct action of ultraviolet (UV) radiation with wavelengths 280, 310, and 365 nm was shown to increase the amplitude of the spontaneous EEG and to potentiate epileptiform activity, whereas the action of subthreshold radiation with wavelengths of 580 and 630 nm caused a reduction of EEG amplitude and inhibition of epileptiform activity. On the basis of the writers' own results and data in the literature it is postulated that the mechanism of action of UV radiation on neocortical electrical activity is based on changes in permeability of neuronal membranes to Na and K ions and subsequent membrane depolarization, whereas the action of visible radiation leads to thermal injury to the neurons in the irradiated zone, inducing irreversible suppression of their activity and a decrease in amplitude of the EEG.Translated from Fiziologicheskii Zhurnal SSSR imeni I. M. Sechenova, Vol. 68, No. 7, pp. 999–1005, July, 1982.     

Cyclic nucleotide metabolism in mouse brain during seizures induced by bicuculline or dibutyryl cyclic guanosine monophosphate

In adult male C57 black mice, intracortical injection of bicuculline (10 μg) elevated cGMP concentrations and produced contralateral clonic seizures. After intraperitoneal injection, bicuculline (10 mg/kg) elevated cGMP concentrations at the earliest time at which paroxysmal EEG activity could be detected. Changes in cAMP concentration followed those events. Further elevations of cGMP concentrations (and now of cAMP as well) were observed during clonic and tonic seizures. Intracortical injections of dibutyryl cGMP produced behavioral and EEG seizures. These data suggest that cGMP plays an important role in bicuculline seizures.     

Effect of lamotrigine on EEG paroxysmal abnormalities and background activity: a computerized analysis

1 Little information is available about the action of lamotrigine (LTG) on EEG paroxysmal abnormalities and background activity. On the contrary, several clinical trials have shown the therapeutic efficacy of the drug in preventing partial and generalized seizures.
2 We performed computerized EEG monitoring in 21 patients suffering from focal and generalized epilepsy before and 4 months after addition of LTG. The anticonvulsant modified the EEG ictal events by reducing their frequency and duration. A statistically significant decrease of the interictal spikes was observed. The decrease involved mainly the spreading component of the interictal events leading to a better spatial definition of the epileptic focus.
3 In the presence of LTG, generalized tonic-clonic attacks were completely controlled, whereas partial seizures were decreased.
4 The EEG background activity was not modified by the addition of the drug.
5 Our findings suggest a specific role for LTG in the generation and propagation processes of epileptiform activity without interfering with the EEG background activity.     

Identifying true brain interaction from EEG data using the imaginary part of coherency.

OBJECTIVE: The main obstacle in interpreting EEG/MEG data in terms of brain connectivity is the fact that because of volume conduction, the activity of a single brain source can be observed in many channels. Here, we present an approach which is insensitive to false connectivity arising from volume conduction. METHODS: We show that the (complex) coherency of non-interacting sources is necessarily real and, hence, the imaginary part of coherency provides an excellent candidate to study brain interactions. Although the usual magnitude and phase of coherency contain the same information as the real and imaginary parts, we argue that the Cartesian representation is far superior for studying brain interactions. The method is demonstrated for EEG measurements of voluntary finger movement. RESULTS: We found: (a) from 5 s before to movement onset a relatively weak interaction around 20 Hz between left and right motor areas where the contralateral side leads the ipsilateral side; and (b) approximately 2-4 s after movement, a stronger interaction also at 20 Hz in the opposite direction. CONCLUSIONS: It is possible to reliably detect brain interaction during movement from EEG data. SIGNIFICANCE: The method allows unambiguous detection of brain interaction from rhythmic EEG/MEG data.     

Memory deficits in an experimental hippocampal epileptiform syndrome in rats

Rats were trained on a light-discrimination task in a Y maze and 7 days later their hippocampi were injected bilaterally with about 5 mouse LD₅₀ of tetanus toxin. This leads to an epileptiform syndrome, in which the animals are hyperreactive and have complex partial seizures for about 4 weeks. When the rat's memories for the Y maze task were tested either 1, 4, 7, or 9 weeks after induction of the epilepsy, they were found to be impaired. The epilepsy thus caused amnesia both when the animals were epileptic and also at a time when the animals were no longer epileptic. It was also found, in another experiment, that similar partial amnesia at 7 weeks after operation was found whether the toxin injection was carried out 20 min, 1 day, or 1 week after initial training. Thus the susceptibility of the memory to disruption by the epilepsy was not dependent on the age of the memory. It is proposed that the amnesia found in this animal model of hippocampal epilepsy is relevant to the important question of whether memory impairments in patients with temporal lobe epilepsy are caused by the epilepsy itself or are side effects of anticonvulsant medication.     

Methods for finding single generators,with application to auditory driving of the human eeg by complex stimuli

A method is presented for searching any number of simultaneous time series (e.g. from different EEG electrodes) for single generators within a frequency band. The method was applied to human EEGs taken during conditions of listening to complex rhythmic (Mozart symphony and chanting) and non-rhythmic (conversation) sounds. The method indicated a tendency towards single generation in the alpha (8–12 Hz) band during the rhythmic conditions. The method was then extended to test for synchrony between the EEG signals and the auditory signal (as a function of frequency). Such synchrony (auditory driving) was indicated during rhythmic conditions in the alpha band.     

Altered generation of spontaneous oscillations in Alzheimer's disease

Slowing of spontaneous alpha oscillations and an anterior shift of a source of alpha activity (8-13 Hz) have been consistently reported in the EEG studies of Alzheimer's disease (AD). It is unknown whether these changes are associated with a gradual shift in location and frequency of existing sources or rather with the involvement of a new set of oscillators. We addressed this question by applying source modeling (minimum current estimates, MCE) to spontaneous alpha activity recorded with a 306-channel MEG system from eleven non-medicated AD patients with mild to moderate cognitive impairment and twelve age-matched controls during the eyes-closed session. AD patients had predominant lower alpha band sources in the temporal regions, whereas in the controls, robust alpha sources were found near the parieto-occipital sulcus. Activation within the parieto-occipital region was significantly weaker, and activation in the right temporal area was significantly enhanced in the AD patients. These results suggest an increased temporal-lobe contribution coinciding with parieto-occipital deficits. We propose that MCE, which provides simultaneous mapping of several oscillatory sources, might be useful for detecting neurophysiological abnormalities associated with AD in combination with other neuropsychological and neurological measures.     

Changes in sleep-wake cycle after chronic exposure to uranium in rats

Uranium is a heavy metal known to induce toxicity in kidneys. It is also known to enter the central nervous system, thus inducing neurophysiological effects, after exposure to relatively high concentrations. The effect of chronic uranium exposure (40 mg l^− 1 in drinking water, for 90 days) on electroencephalographic architecture has been studied on freely moving rats using a telemetry technique. The main effects of uranium on the sleep–wake cycle were an increase in rapid eye movement sleep (REM-sleep) and theta band power during the light period, as early as Day 30 after exposure commenced. The most probable explanation for these effects is that uranium directly affects the brain. This increase in REM-sleep was previously described in human depression or models of chronically stressed rats and it may be assimilated with some protective or compensatory mechanisms.     

Orienting to external versus internal regions of space: consequences of attending in advance versus after the fact

We examined effects of knowing where to attend to-be-remembered information in advance versus after the fact. Participants performed a visuospatial short-term memory task with orienting cues that appeared before or after a memory display and reported whether a probe item had appeared on the cued side. Event-related potentials (ERPs) were recorded for cues, memory displays, and probes. Performance was better in precued versus postcued conditions. ERPs to orienting cues and memory displays were lateralized in relation to the direction of attention in precued but not postcued conditions. ERPs to recognition probes were lateralized, but this was similar between pre- and postcued conditions. Results suggest that we can orient visuospatial attention outwardly to external events and inwardly to remembered events alike, but knowing where to attend information in advance gives a bigger boost to brain and behavior.