Distinct EEG Patterns Research Articles

EEG-based neuroprosthesis control: A step towards clinical practice

This case study demonstrates the coupling of an electroencephalogram (EEG)-based Brain–Computer Interface (BCI) with an implanted neuroprosthesis (Freehand ® system). Because the patient was available for only 3 days, the goal was to demonstrate the possibility of a patient gaining control over the motor imagery-based Graz BCI system within a very short training period. By applying himself to an organized and coordinated training procedure, the patient was able to generate distinctive EEG-patterns by the imagination of movements of his paralyzed left hand. These patterns consisted of power decreases in specific frequency bands that could be classified by the BCI. The output signal of the BCI emulated the shoulder joystick usually used, and by consecutive imaginations the patient was able to switch between different grasp phases of the lateral grasp that the Freehand ® system provided. By performing a part of the grasp-release test, the patient was able to move a simple object from one place to another. The results presented in this work give evidence that Brain–Computer Interfaces are an option for the control of neuroprostheses in patients with high spinal cord lesions. The fact that the user learned to control the BCI in a comparatively short time indicates that this method may also be an alternative approach for clinical purposes.

Epileptogenesis and chronic seizures in a mouse model of temporal lobe epilepsy are associated with distinct EEG patterns and selective neurochemical alterations in the contralateral hippocampus

Major aspects of temporal lobe epilepsy (TLE) can be reproduced in mice following a unilateral injection of kainic acid into the dorsal hippocampus. This treatment induces a non-convulsive status epilepticus and acute lesion of CA1, CA3c and hilar neurons, followed by a latent phase with ongoing ipsilateral neuronal degeneration. Spontaneous focal seizures mark the onset of the chronic phase. In striking contrast, the ventral hippocampus and the contralateral side remain structurally unaffected and seizure-free. In this study, functional and neurochemical alterations of the contralateral side were studied to find candidate mechanisms underlying the lack of a mirror focus in this model of TLE. A quantitative analysis of simultaneous, bilateral EEG recordings revealed a significant decrease of theta oscillations ipsilaterally during the latent phase and bilaterally during the chronic phase. Furthermore, the synchronization of bilateral activity, which is very high in control, was strongly reduced already during the latent phase and the decrease was independent of recurrent seizures. Immunohistochemical analysis performed in the contralateral hippocampus of kainate-treated mice revealed reduced calbindin-labeling of CA1 pyramidal cells; down-regulation of CCK-8 and up-regulation of NPY-labeling in mossy fibers; and a redistribution of galanin immunoreactivity. These changes collectively might limit neuronal excitability in CA1 and dentate gyrus, as well as glutamate release from mossy fiber terminals. Although these functional and neurochemical alterations might not be causally related, they likely reflect long-ranging network alterations underlying the independent evolution of the two hippocampal formations during the development of an epileptic focus in this model of TLE.

„EEG-basierende Kommunikation” - ein neues Konzept zur rehabilitativen Unterstützung von Patienten mit schwerer motorischer Beeinträchtigung

This paper describes a paralyzed patient diagnosed with severe infantile cerebral palsy, trained over a period of several months to use an EEG-based brain-computer interface (BCI) for verbal communication. The patient learned to "produce" two distinct EEG patterns by mental imagery and to use this skill for BCI-controlled spelling. The EEG feedback training was conducted at a clinic for Assisted Communications, supervised from a distant laboratory with the help of a telemonitoring system. As a function of training sessions significant learning progress was found, resulting in an average accuracy level of 70% correct responses for letter selection. At present, "copy spelling" can be performed with a rate of approximately one letter per minute. The proposed communication device, the "Virtual Keyboard", may improve actual levels of communication ability in completely paralyzed patients. "Telemonitoring-assisted" training facilitates clinical application in a larger number of patients.

Neurofeedback in Psychological Practice.

Advances in technology occasionally allow for innovations in the practice of psychology. Neurofeedback is one such modality; in it, individuals learn to change patterns of brain waves through operant conditioning. Research shows that a number of neurological and psychological disorders can be characterized by distinctive EEG patterns and that neurofeedback may help clients to change those patterns. The evidence regarding neurofeedback’s efficacy for attention-deficit/hyperactivity disorder (ADHD), depression, and other disorders is reviewed. Using control group designs, four different research teams have found neurofeedback to be effective for ADHD participants; research on outcomes for other disorders is at a much more preliminary stage. Practicing psychologists are encouraged to explore the potential of this alternative and distinctly psychological modality. Neurofeedback, also known as EEG biofeedback or EEG operant conditioning, is an emerging modality with the potential of becoming an important part of effective psychological practice. Neurofeedback is a process whereby individuals learn to selfregulate their brain waves. Preliminary findings indicate that teaching individuals to alter electrocortical activity may have beneficial effects for attention-deficit/hyperactivity disorder (ADHD). Other research is ongoing to determine the effectiveness of neurofeedback for other disorders as well, including depression and schizophrenia. Its promise notwithstanding, neurofeedback has been virtually ignored by the mainstream investigators and clinicians. Even accounting for the absence of conclusive empirical efficacy, a process that combines two pillars of psychology— operant conditioning and brain function— deserves greater attention from the psychological community. With this article we hope to call attention to this modality by presenting some of the history and research pertaining to brain wave self-regulation.

A Reexamination of PLEDs in the Setting of Status Epilepticus.

Serial EEG During Human Status Epilepticus: Evidence for PLED as an Ictal Pattern Garzon E, Fernandes RM, Sakamoto AC Neurology 2001;57:1175–1183 Objective To analyze the relationship between periodic lateralized epileptiform discharges (PLED) and status epilepticus (SE), to evaluate the relationship between mortality and periodic patterns, and to determine whether a stereotypic sequence of EEG patterns exists during human SE. Methods The authors performed a prospective clinical and electrographic study comprising 62 episodes of SE, 55 patients, and 254 ictal/postictal EEG recordings. Serial daily EEG were obtained in all cases. Results Partial SE was the predominant clinical type. Four distinct ictal EEG patterns were identified: intermittent EEG seizures (IES), merging EEG seizures (MES), continuous ictal discharges (CID), and periodic epileptiform discharges (PED) which could be lateralized (PLED) or bilateral (PBED). IES was the most common ictal pattern. In the same record, only one combination of ictal patterns was observed corresponding to an association of PLED or PBED and MES pattern. Serial EEG demonstrated that approximately one-third of SE resolved before the second EEG, another one-third persisted and maintained the same ictal pattern throughout the entire evolution, and the final one-third showed variable ictal EEG patterns. PLED were also unequivocally associated with epileptic seizures, and in some patients were the initial ictal pattern. Conclusion PLED can be an ictal pattern; and, in contrast to previous observations, no stereotyped sequence of ictal EEG patterns was found. PLED/PBED were not a terminal ictal pattern in every case, and outcome was more related to age and etiology than to specific ictal EEG patterns.

A Reexamination of PLEDs in the Setting of Status Epilepticus

ObjectiveTo analyze the relationship between periodic lateralized epileptiform discharges (PLED) and status epilepticus (SE), to evaluate the relationship between mortality and periodic patterns, and to determine whether a stereotypic sequence of EEG patterns exists during human SE. MethodsThe authors performed a prospective clinical and electrographic study comprising 62 episodes of SE, 55 patients, and 254 ictal/postictal EEG recordings. Serial daily EEG were obtained in all cases. ResultsPartial SE was the predominant clinical type. Four distinct ictal EEG patterns were identified: intermittent EEG seizures (IES), merging EEG seizures (MES), continuous ictal discharges (CID), and periodic epileptiform discharges (PED) which could be lateralized (PLED) or bilateral (PBED). IES was the most common ictal pattern. In the same record, only one combination of ictal patterns was observed corresponding to an association of PLED or PBED and MES pattern. Serial EEG demonstrated that approximately one-third of SE resolved before the second EEG, another one-third persisted and maintained the same ictal pattern throughout the entire evolution, and the final one-third showed variable ictal EEG patterns. PLED were also unequivocally associated with epileptic seizures, and in some patients were the initial ictal pattern. ConclusionPLED can be an ictal pattern; and, in contrast to previous observations, no stereotyped sequence of ictal EEG patterns was found. PLED/PBED were not a terminal ictal pattern in every case, and outcome was more related to age and etiology than to specific ictal EEG patterns.

Variation in Effective Stimulus Patterns for Induction of Long-Term Potentiation Across Different Layers of Rat Entorhinal Cortex

Neuronal activities in superficial (II and III) and deep (V and VI) layers of the entorhinal cortex (EC) are preferentially modulated by theta and sharp wave (SPW) EEG, respectively. We investigated the possibility that distinct EEG patterns represent optimal stimulus patterns for induction of long-term potentiation (LTP) in different layers of the EC. We examined effects of three different stimulation patterns on LTP induction in layers I, II-III, and V of medial EC slices of the rat. The stimulation patterns we used were a single, long high-frequency train (1 sec at 100 Hz, repeated 3x), theta burst stimulation [TBS; 10 bursts (four pulses, 100 Hz) at 5 Hz, repeated 3x], and SPW-like burst stimulation [ SPWBS; three bursts (20 pulses, 200 Hz) at 2 Hz, repeated 6x]. Similar degrees of LTP were induced by the three stimulation patterns in layer I. In layers II--III and layer V, however, the largest degrees of LTP were induced by TBS and SPWBS, respectively. These results suggest that burst stimulation constructed to mimic naturally occurring patterns of neuronal activity in the corresponding layer is optimal for LTP induction in layers II-III and layer V of the EC. The differences may play important roles in shaping hippocampal-neocortical interactions in encoding and retrieval of memory.

Serial EEG during human status epilepticus: evidence for PLED as an ictal pattern.

To analyze the relationship between periodic lateralized epileptiform discharges (PLED) and status epilepticus (SE), to evaluate the relationship between mortality and periodic patterns, and to determine whether a stereotypic sequence of EEG patterns exists during human SE. The authors performed a prospective clinical and electrographic study comprising 62 episodes of SE, 55 patients, and 254 ictal/postictal EEG recordings. Serial daily EEG were obtained in all cases. Partial SE was the predominant clinical type. Four distinct ictal EEG patterns were identified: intermittent EEG seizures (IES), merging EEG seizures (MES), continuous ictal discharges (CID), and periodic epileptiform discharges (PED) which could be lateralized (PLED) or bilateral (PBED). IES was the most common ictal pattern. In the same record, only one combination of ictal patterns was observed corresponding to an association of PLED or PBED and MES pattern. Serial EEG demonstrated that approximately one-third of SE resolved before the second EEG, another one-third persisted and maintained the same ictal pattern throughout the entire evolution, and the final one-third showed variable ictal EEG patterns. PLED were also unequivocally associated with epileptic seizures, and in some patients were the initial ictal pattern. PLED can be an ictal pattern; and, in contrast to previous observations, no stereotyped sequence of ictal EEG patterns was found. PLED/PBED were not a terminal ictal pattern in every case, and outcome was more related to age and etiology than to specific ictal EEG patterns.

EEG criteria predictive of complicated evolution in idiopathic rolandic epilepsy.

Although so-called "benign" epilepsy with centrotemporal spikes (BECTS) always has an excellent prognosis with regard to seizure remission, behavioral problems and cognitive dysfunctions may sometimes develop in its course. To search for clinical or EEG markers allowing early detection of patients prone to such complications, the authors conducted a prospective study in a cohort of unselected patients with BECTS. In 35 children with BECTS, academic, familial, neurologic, neuropsychological, and wake and sleep EEG evaluations were repeated every 6 to 12 months from the beginning of the seizure disorder up to complete recovery. In 25 of 35 patients (72%), behavioral and intellectual functioning remained unimpaired. In 10 of 35 patients (28%), educational performance and familial maladjustment occurred. These sociofamilial problems were correlated with impulsivity, learning difficulties, attention disorders, and minor (7/35 cases, 20%) or serious (3/35 cases, 8%) auditory-verbal or visual-spatial deficits. Worsening phases started 2 to 36 months after onset and persisted for 9 to 39 months. Occurrence of atypical evolutions was significantly correlated with five qualitative and one quantitative interictal EEG pattern: intermittent slow-wave focus, multiple asynchronous spike-wave foci, long spike-wave clusters, generalized 3-c/s "absence-like" spike-wave discharges, conjunction of interictal paroxysms with negative or positive myoclonia, and abundance of interictal abnormalities during wakefulness and sleep. Clinical deterioration was not linked with seizure characteristics or treatment. Different combinations of at least three of six distinctive interictal EEG patterns and their long-lasting (> or =6-month) persistence seem to be the hallmarks of patients with BECTS at risk for neuropsychological impairments.

The fundamental neural mechanisms of electroencephalography

We are at an interesting time in the evolution of the EEG. Studies are opening the door to understanding the intrinsic neuronal properties and network operations responsible for the generation of EEG oscillations. I will review some of our knowledge regarding the physiology of the normal and abnormal EEG. Both epileptic and non-epileptic activity will be discussed. Less is known about the latter, because of difficulties in developing appropriate models. The major dichotomy for both types of EEG phenomenon will be focal and generalized (or widespread. Certain distinctive abnormal EEG patterns including burst suppression, periodic phenomena and intermittent rhythmic delta will also be addressed.

Distribution of parvalbumin-immunoreactive neurons in brain correlates with hippocampal and temporal cortical pathology in Creutzfeldt-Jakob disease.

There is a distinctive pattern of hippocampal involvement in Creutzfeldt-Jakob disease (CJD) and evidence for selective vulnerability of GABAergic neurons in experimental and human prion disease. We studied hippocampus and temporal cortex from human CJD and control autopsy brains and surgical cryptogenic temporal lobe epilepsy specimens for distribution and density of parvalbumin (PV) and calbindin-D28K (Cal) -positive neurons that are subpopulations of GABAergic neurons. Pathology was evaluated semiquantitatively in 8 regions in 23 CJD brains for severity of spongiform change, astrogliosis and pathological prion protein deposition. In CJD, pathology was severe in pre-parasubiculum and temporal cortex, and little or absent in CA1-4; PV+ neurons were severely reduced or absent in all cases, whereas Cal+ neurons were largely preserved. In controls, the density of PV+ neurons was highest in pre-parasubiculum and temporal cortex, and lowest in CA1-4. In cTLE, loss of PV+ neurons was seen only in CA1-4. The diffuse and severe loss of PV+ neurons in CJD, and the topographical correlation of tissue lesioning in CJD with density of PV+ neurons in controls suggest selective vulnerability and early loss of this subset of inhibitory neurons in CJD. This might relate to characteristic CJD symptoms such as myoclonus and the distinctive EEG pattern.

Electrocortical distinction of vocabulary types

Psycholinguistic theories propose that words of the 2 major vocabulary classes, content (open-class) and function (closed-class) words, are computationally distinct and have different neuronal generators. This predicts distinct EEG patterns elicited by words of these 2 classes. To test this prediction, content and function words, together with matched pseudowords, were presented in a lexical decision task (where subjects had to decide whether stimuli were meaningful words or not). Evoked potentials were recorded from 17 electrodes 12 of which were located in close vicinity of the perisylvian cortices. Already 160 msec post stimulus onset, substantial differences in activity patterns distinguish the 2 vocabulary classes. A hemisphere by word class interaction revealed interhemispheric differences for function words but not for content words. Potentials evoked by function words were more negative over the left hemisphere compared to the right. These results evidence that brain mechanisms underlying function and content word processing are different. The following explanation of the data is proposed: content words correspond to neuronal assemblies equally distributed over both hemispheres, while assemblies corresponding to function words are strongly lateralized to the left hemisphere and primarily located in the perisylvian region.

Use of computerized electroencephalographic monitoring during aneurysm surgery.

The clinical usefulness of intraoperative electroencephalographic (EEG) monitoring of cerebral perfusion during aneurysm surgery has received little attention, primarily due to problems with electrode placement over the operative site, which is the area of maximal risk. In this report, 27 patients undergoing surgery for anterior circulation aneurysms were monitored intraoperatively with a two-channel computerized EEG complex using a bilateral frontal-occipital montage. In 16 patients, a normal EEG pattern was observed throughout surgery; all 16 awoke neurologically intact and their postoperative angiograms did not reveal cerebral vasospasm. In the other 11 patients, one of two patterns of persistent EEG abnormalities was identified. 1) In six of these patients a marked attenuation of EEG activity was observed ipsilaterally which coincided with various intraoperative events including brain retraction, hypotension, and aneurysm dissection/clipping. Five of these six patients awoke with new neurological deficits which persisted beyond 12 hours in two, both of whom had angiographically proven vasospasm 24 hours after surgery. 2) In the remaining five patients, a distinct abnormal EEG pattern consisting of marked hyperactivity in the delta, theta, and alpha frequency ranges was observed ipsilaterally. Four of these five patients had a poor neurological outcome and vasospasm on their angiogram 24 hours after surgery. Thus, EEG monitoring which spans the operative area during aneurysm surgery is practicable and appears to be of value in the detection of compromised cerebral perfusion during aneurysm surgery. The possible significance of the two abnormal EEG patterns identified in this report is discussed.

Inhibition of penicillin-induced EEG discharge by low doses of morphine or naloxone in the rabbit. Evidence for a possible non-opioid receptor-mediated mechanism at the sensorimotor cortex

In rabbits, pretreatment by intravenous (IV) and intracortical (IC) routes with low doses of morphine (250 μg/kg IV or 60 pmoles/rabbit IC) and naloxone (1–50 μg/kg IV or 0.3 pmoles/rabbit IC) antagonizes the EEG and behavioural seizures due to the IC injection of penicillin (150 Units) at the level of the sensorimotor cortex. Pretreatment with naloxone (20 μg/kg IV) did not alter the anticonvulsant effect of morphine (250 μg/kg IV). The similar anticonvulsant effect of the two drugs together with the absence of any antagonism by naloxone on the effect of morphine seem to suggest that both drugs act through a non-opioid receptor-mediated mechanism. Further, in light of the low effective doses of the drugs and of the absence of any additive effect after their combined administration, one might speculate that morphine and naloxone do not act through different pharmacological receptors. However, the presence of distinct EEG patterns with either morphine or naloxone, injected IC and IV, in animals fully protected against penicillin-induced seizures, does not seem to be in favour of the latter possibility.

EEG during masturbation and ejaculation.

The occurrence of a distinctive EEG pattern specifically related to sexual arousal and orgasm would provide a reliable and convenient means of identifying such events in the laboratory and would also provide clues to cerebral structures involved in the processes. EEG-polygraph recordings were obtained under rigorously controlled conditions in four normal male subjects during masturbation and ejaculation. The EEG data were subjected to both impressionistic and quantitative analyses. They showed no remarkable changes during the sequence of relevant physiological responses. The sole effect was a slight depression of alpha activity, a well-known nonspecific effect associated with changes in attention and arousal. Examination of the literature shows little agreement among reported results of studies of EEG changes during orgasm. It is likely that at least some reported changes were artifactual. It is concluded that the case for the existence of EEG changes specifically related to sexual arousal and orgasm remains unproven.

A distinctive electrographic entity: bursts of rhythmical temporal theta.

The goal of this study was to investigate the electro-clinical correlations of a distinctive EEG pattern: bursts of rhythmic temporal theta (BORTT). Patients (260) with this pattern were compared to 4 control groups. The peak age in patients with BORTT was in the 50's, appearing especially in black females. The incidence of this pattern in our randomly selected patient group was significantly greater than in a group without evidence of organic cerebral disease. BORTT had a marked preference for the left temporal area (93%), as opposed to the right (30%). In 1/3 of patients, no other EEG finding appeared and in an equal number other mild slow wave abnormalities were seen. Evidence of some kind of vascular disorder (33%) or trauma (16%) was found in nearly 1/2 of the BORTT patients, but the pattern is likely associated with may kinds of etiologies. In conclusion, BORTT likely represents a mild slow wave abnormality, especially of the left temporal lobe in adults, indicating a slight neurophysiological disturbance of varying etiology, but often of vascular origin.

Coexistence of triphasic waves and alpha-coma pattern

The coexistence of triphasic waves and alpha-coma pattern in an EEG was observed in a 67-year-old comatose man following cardiopulmonary arrest, while his brain stem functions were intact. Although they may be diagnostically and prognostically significant, these EEG findings can be hard to recognize. These two distinct EEG patterns do not seem to be mutually exclusive.