Emma M. Whitham

Thinking activates EMG in scalp electrical recordings.

OBJECTIVE Fast electrical rhythms in the gamma range (30-100Hz) in scalp (but not intracranial) recordings are predominantly due to electromyographic (EMG) activity. We hypothesized that increased EMG activity would be augmented by mental tasks in proportion to task difficulty and the requirement of these tasks for motor or visuo-motor output. METHODS EEG was recorded in 98 subjects whilst performing cognitive tasks and analysed to generate power spectra. In four other subjects, neuromuscular blockade was achieved pharmacologically providing EMG-free spectra of EEG at rest and during mental tasks. RESULTS In comparison to the paralysed condition, power of scalp electrical recordings in the gamma range varied in distribution, being maximal adjacent to cranial or cervical musculature. There were non-significant changes in mean gamma range activity due to mental tasks in paralysed subjects. In normal subjects, increases in scalp electrical activity were observed during tasks, without relationship to task difficulty, but with tasks involving limb- or eye-movement having higher power. CONCLUSIONS Electrical rhythms in the gamma frequency range recorded from the scalp are inducible by mental activity and are largely due to EMG un-related to cognitive effort. EMG varies with requirements for somatic or ocular movement more than task difficulty. SIGNIFICANCE Severe restrictions exist on utilizing scalp recordings for high frequency EEG.

Surface Laplacian of Central Scalp Electrical Signals is Insensitive to Muscle Contamination

The objective of this paper was to investigate the effects of surface Laplacian processing on gross and persistent electromyographic (EMG) contamination of electroencephalographic (EEG) signals in electrical scalp recordings. We made scalp recordings during passive and active tasks, on awake subjects in the absence and in the presence of complete neuromuscular blockade. Three scalp surface Laplacian estimators were compared to left ear and common average reference (CAR). Contamination was quantified by comparing power after paralysis (brain signal, B) with power before paralysis (brain plus muscle signal, B+M). Brain:Muscle (B:M) ratios for the methods were calculated using B and differences in power after paralysis to represent muscle (M). There were very small power differences after paralysis up to 600 Hz using surface Laplacian transforms (B:M >; 6 above 30 Hz in central scalp leads). Scalp surface Laplacian transforms reduce muscle power in central and pericentral leads to less than one sixth of the brain signal, two to three times better signal detection than CAR. Scalp surface Laplacian transformations provide robust estimates for detecting high-frequency (gamma) activity, for assessing electrophysiological correlates of disease, and also for providing a measure of brain electrical activity for use as a standard in the development of brain/muscle signal separation methods.

The symbol of modern medicine: why one snake is more than two.

Western culture demands integrity, personal sacrifice, and compassion from its physician healers. This powerful social expectation predates Christianity and has its origins in the heroic and mythologic traditions of ancient Greece. The heroic, and later mythical, figure of Asklepios was a major focus of ancient Greco-Roman medical tradition from perhaps as early as 1200 BC (1, 2) until 500 AD (3-14). The mortal herophysician Asklepios, mentioned in Homers Iliad, exemplified the ideal Greek physician (2). Later, as Asklepios was deified and worshipped, these traditions of patient care spread throughout Greece and, subsequently, the vast Roman Empire (4-6). Asklepios came to be recognized as the god of medicine and the mythical son of Apollo whose healing power Asklepios had inherited and expanded (3-8). The cult of Asklepios and his family seems to have originated at Trikka in Thessaly; by Roman times, hundreds of ancient temple complexes, called Asklepieions, had been built throughout the Greco-Roman world (6). The Asklepieions of Epidavros, Kos, and Pergamon were particularly extensive and elaborate, resembling a cross between a sanatorium and a modern hospital. In times of illness, Asklepios was the focus of ancient Greco-Roman supplication, particularly for the poor and disregarded (4). Many early Greek physicians claimed direct descent from the herophysician Asklepios, proclaiming themselves a family of Asklepiades. Hippokrates (circa 460 to 377 BC) proudly claimed descent from Asklepios via Poldaleiros, the skillful physician son of Asklepios (4); indeed, Plato (circa 427 to 347 BC) often referred to Hippokrates as the Asklepiade (5). With the spread of the cult of the god Asklepios, the term Asklepiade was applied more generically, and Asklepios was seen as the patron of physicians and the guardian of the medical craft. The great physician Galen (circa 129 to 216 AD) began his training as an attendant at the Asklepieion of Pergamon (15) and in his writings referred to Asklepios as his ancestral God (4, 16). The opening lines of the Hippokratic Oath clearly reveal the central role occupied by Asklepios and his mythologic daughters, Hygieia and Panakeia, in the hearts and minds of the ancients: I swear by Apollo Physician and Asklepios and Hygieia and Panakeia and all the gods and goddesses, making them my witnesses, that I will fulfil according to my ability and judgement this oath and this covenant (17). Asklepios was commonly depicted on statues, reliefs, coins, and physicians rings holding his Asklepian emblem. Several myths describe how Asklepios chose his symbol (4). In perhaps the most popular tale, Asklepios is examining a man, Glaukos, whom Zeus had recently struck dead with a thunderbolt. During the examination, a snake gliding into the room surprised Asklepios, and he responded by killing it with a blow from his staff. Asklepios was subsequently intrigued by the arrival of a second serpent, which placed certain herbs in the mouth of the dead serpent and thereby restored it to life. Asklepios quickly perceived the lesson, revived Glaukos by recourse to the same herbs, and, as a mark of respect, adopted the serpent coiling about his staff as his emblem (4). The use of the Asklepian motif was very popular throughout antiquity. However, from the early Christian era to the Middle Ages, many of the ancient Greco-Roman gods and symbols were suppressed by the Catholic Church, and uroscopy (or water-casting) came to play an important role in medical diagnosis (18). Thus, from the 6th century until the Renaissance, the urine flask replaced the Asklepian as the symbol of the profession (19). The changes in religious imagination and values that took place after the Reformation in the Protestant countries of northern Europe had direct repercussions on the choice of medical patrons and symbols. As Catholic patron saints of medicine lost favor, they were replaced by the rediscovered symbols of antiquity (7). Subsequently, in countries such as England, the Netherlands, Norway, and Sweden, illustrations, art works, and statues of Asklepios began to proliferate; Asklepios was often accompanied by his mythical daughter, Hygieia, the goddess of health (7). Clearly, Asklepios was no longer worshipped as a divinity; however, because of the intense interest in the symbolism, learning, and traditions of the Greco-Roman period, the Asklepian was again recognized and firmly established as the symbol of medicine (Figure 1). Figure 1. Statues of Asklepios and Hygieia. From the beginning of the 17th century, the figure of Asklepios began appearing on medical medals and calling cards. The same pattern seen in antiquity emerged: The symbol was used only in a medical context, whereas the caduceus, although used by some medical organizations, was associated with other fields, especially commerce, communications, chemistry, and pharmacy (7, 13, 19). The Recent Adoption of the Caduceus as a Medical Symbol In most countries, the Asklepian is firmly established as the symbol of military and civilian medicine (20). Therefore, it is difficult to understand the widespread use of the caduceus in the United States, especially because it is used side by side with the Asklepian motif. For example, the emblem of the U.S. Public Health Service bears the caduceus, whereas the National Library of Medicine and American Medical Association prominently display the Asklepian. Within the military, the badge insignia of the U.S. Army Medical Corps (USAMC) is the caduceus, but its coat of arms, which is that of the U.S. Army Medical Department (USAMEDD) (adopted in 1818), bears the Asklepian (21, 22) (Figure 2). Figure 2. Symbols of the U.S. Army Medical Corps (USAMC). Top. Bottom. So why did the caduceus become inappropriately associated with medicine in the minds of North American doctors in the late 19th century? Some have hypothesized that the reason is related to the use of the caduceus motif by some European publishing houses. In particular, John Churchill of London, the prolific medical publisher, used a caduceus printers mark on the title page of many of the medical and scientific books he exported to the United States (13). The mark may have symbolized Churchills desire to unite medicine and literature because it consisted of two serpents labeled medicina and literis and a motto Irrupta Tenet Copula (unbreakable bond unites) (23). Nevertheless, John Churchill clearly saw the caduceus as his printers mark and not the symbol of medicine because several of his medical books also included prominent representations of the Asklepian (13). In the United States, however, an erroneous mental connection between Churchills caduceus and medical practice seems to have developed. By the late 19th century, several United Statesbased publishing houses, assuming that the caduceus was a symbol of medicine, had copied or adapted Churchills caduceus printers mark and were prominently displaying it in their medical books (13). Apparently, this misunderstanding was sufficiently widespread in the medical community in the United States to have stimulated the publication of papers condemning the adoption of the caduceus and the neglect of the Asklepian (24, 25). The important question to ask is how did the caduceus become popular so quickly in the United States. The role of the USAMC is crucial. In 1902, at the suggestion of an assistant surgeon, Captain Frederick Reynolds, a new uniform code was established, and the caduceus became a collar insignia for all personnel in the USAMC. From Captain Reynolds correspondence with the Surgeon Generals office, it is apparent that he was unaware of the distinction between the caduceus and Asklepian when he recommended the combined use of the cock of Aesculapius and the caduceus. His statement to the Surgeon General that the Medical Corps of several foreign powers, notably the English all displayed the caduceus was also erroneous. In fact, no other western medical military service of that time displayed the caduceus; they all used either the Asklepian or symbols based on the Christian cross (13). Thus, the adoption of the caduceus by the USAMEDD seems to have been simply a misunderstanding of classical mythologic iconography. Ironically, this mistake was almost avoided. In March 1902, when Captain Reynolds initially suggested the switch to the caduceus symbol, the Surgeon General, G.W. Sternberg, dismissed his request outright. However, Captain Reynolds was persistent and, later that year, he sent a second letter to the new Surgeon General, W.H. Forwood; this time, his proposal was approved. Thus, on 17 July 1902, the caduceus of gold was adopted as the branch insignia of the USAMC (13, 26). This faux pas did not go entirely unnoticed in the United States (21, 27, 28). In 1917, Lieutenant Colonel McCulloch, the librarian to the Surgeon General, discovered original documents showing that the coat of arms adopted by the USAMEDD a century earlier had displayed the Asklepian and not the caduceus. McCulloch lamented: I think that in this country we pay too little attention to the historical and humanistic side of things. The caduceus or wand of Mercury now used on the collar of the uniform blouse of the medical corps, has really no medical bearing whatever. It really should be replaced as a corps design by the Aesculapian staff and serpent (21). Why the Caduceus Is an Inappropriate Medical Symbol It is in and through symbols that man, consciously or unconsciously, lives, works and has his being (29). Symbols have power because of their associations and traditions. It is precisely for this reason that the symbol of the blameless physician Asklepios (2), and not the caduceus of Hermes (Latin, Mercury), is an appropriate emblem for the ideals of modern medicine. It is easy to appreciate the inaptness of the caduceus as a medical symbol, given an understanding of the role and attributes assigned to Hermes in ancient mytholo

Surface Laplacian of scalp electrical signals and independent component analysis resolve EMG contamination of electroencephalogram

The serious impact of electromyogram (EMG) contamination of electroencephalogram (EEG) is well recognised. The objective of this research is to demonstrate that combining independent component analysis with the surface Laplacian can eliminate EMG contamination of the EEG, and to validate that this processing does not degrade expected neurogenic signals. The method involves sequential application of ICA, using a manual procedure to identify and discard EMG components, followed by the surface Laplacian. The extent of decontamination is quantified by comparing processed EEG with EMG-free data that was recorded during pharmacologically induced neuromuscular paralysis. The combination of the ICA procedure and the surface Laplacian, with a flexible spherical spline, results in a strong suppression of EMG contamination at all scalp sites and frequencies. Furthermore, the ICA and surface Laplacian procedure does not impair the detection of well-known, cerebral responses; alpha activity with eyes-closed; ERP components (N1, P2) in response to an auditory oddball task; and steady state responses to photic and auditory stimulation. Finally, more flexible spherical splines increase the suppression of EMG by the surface Laplacian. We postulate this is due to ICA enabling the removal of local muscle sources of EMG contamination and the Laplacian transform being insensitive to distant (postural) muscle EMG contamination.

Automatic determination of EMG-contaminated components and validation of independent component analysis using EEG during pharmacologic paralysis

OBJECTIVE Validate independent component analysis (ICA) for removal of EMG contamination from EEG, and demonstrate a heuristic, based on the gradient of EEG spectra (slope of graph of log EEG power vs log frequency, 7-70 Hz) from paralysed awake humans, to automatically identify and remove components that are predominantly EMG. METHODS We studied the gradient of EMG-free EEG spectra to quantitatively inform the choice of threshold. Then, pre-existing EEG from 3 disparate experimental groups was examined before and after applying the heuristic to validate that the heuristic preserved neurogenic activity (Berger effect, auditory odd ball, visual and auditory steady state responses). RESULTS (1) ICA-based EMG removal diminished EMG contamination up to approximately 50 Hz, (2) residual EMG contamination using automatic selection was similar to manual selection, and (3) task-induced cortical activity remained, was enhanced, or was revealed using the ICA-based methodology. CONCLUSION This study further validates ICA as a powerful technique for separating and removing myogenic signals from EEG. Automatic processing based on spectral gradients to exclude EMG-containing components is a conceptually simple and valid technique. SIGNIFICANCE This study strengthens ICA as a technique to remove EMG contamination from EEG whilst preserving neurogenic activity to 50 Hz.

Visual experiences during paralysis

Rationale: Paralyzed human volunteers (n = 6) participated in several studies the primary one of which required full neuromuscular paralysis while awake. After the primary experiment, while still paralyzed and awake, subjects undertook studies of humor and of attempted eye-movement. The attempted eye-movements tested a central, intentional component to one’s internal visual model and are the subject of this report. Methods: Subjects reclined in a supportive chair and were ventilated after paralysis (cisatracurium, 20 mg intravenously). In illumination, subjects were requested to focus alternately on the faces of investigators standing on the left and the right within peripheral vision. In darkness, subjects were instructed to look away from a point source of light. Subjects were to report their experiences after reversal of paralysis. Results: During attempted eye-movement in illumination, one subject had an illusion of environmental movement but four subjects perceived faces as clearly as if they were in central vision. In darkness, four subjects reported movement of the target light in the direction of attempted eye-movements and three could control the movement of the light at will. Conclusion: The hypothesis that internal visual models receive intended ocular-movement-information directly from oculomotor centers is strengthened by this evidence.

Constitutive spectral EEG peaks in the gamma range: suppressed by sleep, reduced by mental activity and resistant to sensory stimulation.

Objective: In a systematic study of gamma activity in neuro-psychiatric disease, we unexpectedly observed distinctive, apparently persistent, electroencephalogram (EEG) spectral peaks in the gamma range (25–100 Hz). Our objective, therefore, was to examine the incidence, distribution and some of the characteristics of these peaks. Methods: High sample-rate, 128-channel, EEG was recorded in 603 volunteers (510 with neuropsychiatric disorders, 93 controls), whilst performing cognitive tasks, and converted to power spectra. Peaks of spectral power, including in the gamma range, were determined algorithmically for all electrodes. To determine if peaks were stable, 24-h ambulatory recordings were obtained from 16 subjects with peaks. In 10 subjects, steady-state responses to stimuli at peak frequency were compared with off-peak-frequency stimulation to determine if peaks were a feature of underlying network resonances and peaks were evaluated with easy and hard versions of oddball tasks to determine if peaks might be influenced by mental effort. Results: 57% of 603 subjects exhibited peaks >2 dB above trough power at or above 25 Hz. Larger peaks (>5 dB) were present in 13% of subjects. Peaks were distributed widely over the scalp, more frequent centrally. Peaks were present through the day and were suppressed by slow-wave-sleep. Steady-state responses were the same with on- or off-peak sensory stimulation. In contrast, mental effort resulted in reductions in power and frequency of gamma peaks, although the suppression did not correlate with level of effort. Conclusions: Gamma EEG can be expressed constitutively as concentrations of power in narrow or wide frequency bands that play an, as yet, unknown role in cognitive activity. Significance: These findings expand the described range of rhythmic EEG phenomena. In particular, in addition to evoked, induced and sustained gamma band activity, gamma activity can be present constitutively in spectral peaks.

Improved artefact removal from EEG using Canonical Correlation Analysis and spectral slope

BACKGROUND Contamination of scalp measurement by tonic muscle artefacts, even in resting positions, is an unavoidable issue in EEG recording. These artefacts add significant energy to the recorded signals, particularly at high frequencies. To enable reliable interpretation of subcortical brain activity, it is necessary to detect and discard this contamination. NEW METHOD We introduce a new automatic muscle-removal approach based on the traditional Blind Source Separation-Canonical Correlation Analysis (BSS-CCA) method and the spectral slope of its components. We show that CCA-based muscle-removal methods can discriminate between signals with high correlation coefficients (brain, mains artefact) and signals with low correlation coefficients (white noise, muscle). We also show that typical BSS-CCA components are not purely from one source, but are mixtures from multiple sources, limiting the performance of BSS-CCA in artefact removal. We demonstrate, using our paralysis dataset, improved performance using BSS-CCA followed by spectral-slope rejection. RESULT This muscle removal approach can reduce high-frequency muscle contamination of EEG, especially at peripheral channels, while preserving steady-state brain responses in cognitive tasks. COMPARISON WITH EXISTING METHODS This approach is automatic and can be applied on any sample of data easily. The results show its performance is comparable with the ICA method in removing muscle contamination and has significantly lower computational complexity. CONCLUSION We identify limitations of the traditional BSS-CCA approach to artefact removal in EEG, propose and test an extension based on spectral slope that makes it automatic and improves its performance, and results in performance comparable to competitors such as ICA-based artefact removal.

Evaluation of a minimum-norm based beamforming technique, sLORETA, for reducing tonic muscle contamination of EEG at sensor level

BACKGROUND Cranial and cervical muscle activity (electromyogram, EMG) contaminates the surface electroencephalogram (EEG) from frequencies below 20 through to frequencies above 100Hz. It is not possible to have a reliable measure of cognitive tasks expressed in EEG at gamma-band frequencies until the muscle contamination is removed. NEW METHOD In the present work, we introduce a new approach of using a minimum-norm based beamforming technique (sLORETA) to reduce tonic muscle contamination at sensor level. Using a generic volume conduction model of the head, which includes three layers (brain, skull, and scalp), and sLORETA, we estimated time-series of sources distributed within the brain and scalp. The sources within the scalp were considered to be muscle and discarded in forward modelling. RESULT (1) The method reduced EMG contamination, more strongly at peripheral channels; (2) task-induced cortical activity was retained or revealed after removing putative muscle activity. COMPARISON WITH EXISTING METHODS This approach can decrease tonic muscle contamination in scalp measurements without relying on time-consuming processing of expensive MRI data. In addition, it is competitive to ICA in muscle reduction and can be reliably applied on any length of recorded data that captures the dynamics of the signals of interest. CONCLUSION This study suggests that sLORETA can be used as a method to quantitate cranial muscle activity and reduce its contamination at sensor level.

Resting cranial and upper cervical muscle activity is increased in patients with migraine

OBJECTIVE To compare comprehensive measures of scalp-recorded muscle activity in migraineurs and controls. METHOD We used whole-of-head high-density scalp electrical recordings, independent component analysis (ICA) and spectral slope of the derived components, to define muscle (electromyogram-containing) components. After projecting muscle components back to scalp, we quantified scalp spectral power in the frequency range, 52-98 Hz, reflecting muscle activation. We compared healthy subjects (n = 65) and migraineurs during a non-headache period (n = 26). We also examined effects due to migraine severity, gender, scalp-region and task (eyes-closed and eyes-open). We could not examine the effect of pre-ictal versus inter-ictal versus post-ictal as this information was not available in the pre-existing dataset. RESULTS There was more power due to muscle activity (mean ± SEM) in migraineurs than controls (respectively, -13.61 ± 0.44 dB versus -14.73 ± 0.24 dB, p = 0.028). Linear regression showed no relationship between headache frequency and muscle activity in any combination of region and task. There was more power during eyes-open than eyes-closed (respectively, -13.42 ± 0.34 dB versus -14.92 ± 0.34 dB, p = 0.002). CONCLUSIONS There is an increase in cranial and upper cervical muscle activity in non-ictal migraineurs versus controls. This raises questions of the role of muscle in migraine, and the possible differentiation of non-ictal phases. SIGNIFICANCE This provides preliminary evidence to date of possible cranial muscle involvement in migraine.