Telemetry of several biological signals from behaving animals

A telemetry device is described for recording ECG, EMG, EEG, multiple and single unit activity from central nervous system. It implies the use of a FET input operational amplifier and an FM oscillator. It can be used with different electrodes and in many animal species when behavioral studies and completely unrestrained subjects are requested.     

A NEW METHOD FOR DETECTING EYE MOVEMENT IN SLEEP

A new method of detecting eye movements (EMs) during sleep is described. The method consists of an electromechanical measurement using micro-miniaturized silver cup electrodes. These electrodes, when placed on the eyelid, produce electro-oculographic (EOG) recordings similar to the usual electrical method. The eyelid method offers the advantage of a relatively “clean” recording showing only EMs and movement artifact, with no intermingling of EEG and EOG. Furthermore, the method is at least one and one half times as sensitive as the usual EOG technique. In addition to these two special advantages, it also offers the features of conventional methods, convenience of DC coupling, independence from signal converters, ease of analyzing EM directionality, and durability despite the small size of the electrodes. Fabrication of the electrodes, recording configurations, and simultaneous comparisons to both the usual EOG technique and to a strain gauge method are described.     

Electromyographic studies of neck muscles in the intact cat

Summary Natural head movements in alert, unrestrained cats were studied using video-filming, videofluoroscopy and electromyographic (EMG) recording methods. In each cat, up to sixteen neck muscles or neck-muscle compartments were implanted with recording electrodes. Patterns of muscle recruitment were examined during systematically-selected behavioral epochs in which the cat held a range of stationary postures, and when it performed volitional and exploratory behaviors such as flexion-extension or turning, grooming, eating, or headshaking. Patterns of muscular activity were interpreted with reference to simultaneous video images of head and neck movements. In separate, videofluoroscopic analysis, flexion-extension movements were examined to gain insight into the underlying movements of the skull and cervical vertebrae. These and other movements were found commonly to depend upon changes in joint angles between lower as well as upper cervical joints. Stationary postures in which the neck was held vertically were consistently associated with tonic EMG activity in only two long dorsal muscles, biventer cervicis and occipitoscapularis. Less consistent activity was also present in dorsal intervertebral muscles crossing lower cervical joints. When the neck was held horizontally, the long dorsal muscles increased their EMG activity and moderate activity was also recorded in deeper intervertebral and suboccipital muscles. When flexion-extension occurred around upper cervical joints, greatest activity was recorded in rectus capitis posterior and complexus, but when it involved the lower cervical joints, large changes in EMG activity could also be detected in biventer cervicis, occipitoscapularis, and the intervertebral muscles crossing lower cervical joints. During specialized, sagittal-plane movements such as grooming, well-defined patterns of synergy could be recognized that varied according to the degree of involvement of upper and lower cervical joint-sets. Movements in the horizontal plane were associated with EMG activity in a largely different subset of neck muscles including splenius, longissimus capitis and obliquus capitis inferior. The levels of EMG activity during flexion-extension or turning movements were much lower than those observed during other more vigorous behaviors, such as head shaking. Some neck muscles, such as clavotrapezius and sternomastoideus, could only be recruited during forceful or ballistic head movements. Results showed that the patterns of muscular activation were linked not only to the speed and trajectory of the movements of the skull, but also to the kinematics of the motion occurring across different parts of the cervical column.     

Elimination of electrocardiogram artifacts from electroencephalogram records by using the simultaneously recorded electrocardiograph data

We developed a simple method to eliminate electrocardiogram (ECG) artifacts from electroencephalogram (EEG) records by using simultaneously recorded ECG data. The raw EEG data, the real EEG data and the ECG data were regarded as multi-dimensional vectors Ea, Er and C, respectively. Also, the ECG data, with reduced amplitude whose coefficient was denoted as 'k', were assumed to be overlapped on the real EEG. These assumptions introduced the equations [Ea = Er + k.C], [Er.C = 0] and finally [k = Ea. C/C.C]. This calculation method was implemented by a Macintosh computer using data exported from digital EEG recordings (sampled at 200 Hz with 16-bit resolution). In several subjects, sampling intervals of 5 or 10 seconds for calculation succeeded in eliminating ECG artifacts. However, regardless of the sampling interval, this elimination condition was not always efficient in several other subjects, including a brain-dead patient. It was suggested that the ECG data used were insufficient for the calculation, because only one hand-to-hand reference was used for simultaneous recording, as usual. This one ECG reference was able to express only one ECG projection. Then two other hand-to-foot references of ECG were added to the recordings, and the elimination procedure was performed using all of the simultaneously recorded ECG data at the three references. Consequently, elimination was much improved in most subjects, including the brain-dead patient. Our method may be useful for eliminating ECG artifacts without changing reference electrodes.     

Observations on normal EEG activity in different brain regions of the unrestrained swine

This methodological and electrophysiological study was undertaken with the aim of obtaining possibilities for evaluating objectively the ethical value of using high concentration CO2 inhalation as pre-slaughter anaesthesia for swine. A technique for implantation of recording electrodes into the porcine neocortex and limbic system is described, as are results of EEG recording from these brain regions in the unrestrained animal. In addition to expected desynchronized activity in the awake animal, bilateral recordings from the frontal neocortex revealed the irregular occurrence of 'sleep spindle' during apparent non-REM sleep. The 'spindles' were sometimes unilateral, and when bilaterally simultaneous, the amplitude was often larger in one of the hemispheres. The EEG recorded from the dorsal hippocampus was characterized by theta-wave activity. The offering of food to the hungry animal, and subsequent brief feeding periods, were associated with marked accentuation of this theta activity. Recording via electrodes placed within the amygdaloid nuclear complex showed high-frequency activity irregularly interrupted by slow waves. However, if one of the 'amygdaloid' twin electrodes hit the ventral pole of the hippocampus, theta activity was dominant. Electrodes placed adjacent to the amygdaloid nuclei in the pyriform cortex exhibited a basic awake activity similar to that recorded from these nuclei. During apparent non-REM sleep, however, trains of slow waves were seen simultaneously with the appearance of 'sleep spindles' in the ipsilateral neocortex.     

A multichannel telemetry system for recording cardiovascular neural signals.

A multichannel telemetry system was developed for use with chronically instrumented unrestrained cats. This system can simultaneously record efferent and afferent cardiovascular neural signals, bioelectrical noise arising near the electrode recording the neural signals, EEG, ECG, and a standard calibration signal. The miniature (18 cm3), lightweight (24 g), telemeter is a five-channel, time-multiplexed, pulse width modulation (PWM)/FM device employing a high frequency subcarrier (60 kHz) and two sampling frequencies (30 kHz and 6 kHz). The device is powered by two small 120 mA . h silver oxide cells; it has an indoor transmission range of 10 m and can operate for 48 h. One channel transmits a standard signal (a square wave of 100 Hz and 200 mVp-p) used to monitor and regulate the system's performance. When the variation in either the amplitude or frequency of the standard signal is greater than 10% of the control value, the transmitted bioelectrical signals are automatically discarded.     

Instrumentation for the measurement of electric brain responses to transcranial magnetic stimulation

There is described a 60-channel EEG acquisition system designed for the recording of scalp-potential distributions starting just 2.5ms after individual transcranial magnetic stimulation (TMS) pulses. The amplifier comprises gain-control and sample-and-hold circuits to prevent large artefacts from magnetically induced voltages in the leads. The maximum amplitude of the stimulus artefact during the 2.5ms gating period is 1.7 μV, and 5 ms after the TMS pulse it is only 0.9 μV. It is also shown that mechanical forces to the electrodes under the stimulator coil are a potential source of artefacts, even though, with chlorided silver wire and Ag/AgCl-pellet electrodes, the artefact is smaller than 1 μV. The TMS-compatible multichannel EEG system makes it possible to locate TMS-evoked electric activity in the brain.     

Instrumentation for the measurement of electric brain responses to transcranial magnetic stimulation

There is described a 60-channel EEG acquisition system designed for the recording of scalp-potential distributions starting just 2.5ms after individual transcranial magnetic stimulation (TMS) pulses. The amplifier comprises gain-control and sample-and-hold circuits to prevent large artefacts from magnetically induced voltages in the leads. The maximum amplitude of the stimulus artefact during the 2.5ms gating period is 1.7 μV, and 5 ms after the TMS pulse it is only 0.9 μV. It is also shown that mechanical forces to the electrodes under the stimulator coil are a potential source of artefacts, even though, with chlorided silver wire and Ag/AgCl-pellet electrodes, the artefact is smaller than 1 μV. The TMS-compatible multichannel EEG system makes it possible to locate TMS-evoked electric activity in the brain.     

Implanted strain gauge and EMG amplifier to record motor behavior in unrestrained rats

We report a technique for recording EMG from a specific axial muscle with concomitant recording of an independent measure of axial movement during behavioral activity elicited by stimulation applied to awake unrestrained rats. EMG signals are led from bipolar teflon-coated tungsten wires (50 μ diameter) to a well-insulated FET input operational amplifier implanted subcutaneously. At the same time, changes are recorded in the resistance of a small mercury-in-silastic strain gauge stretched between appropriate vertebral dorsal spines. Differential amplification of the EMG in situ has been found to provide a high gain output signal which is relatively free from movement-related artifact. Satisfactory recordings have been obtained for up to 10 days from individual animals and both devices can be re-used.     

Co-firing of levator palpebrae and masseter muscles links the masticatory and oculomotor system in humans

Simultaneous co-firing of the levator palpebrae (LP) and pterygoid muscles were recorded in Marcus Gann Syndrome (MGS) patients in early clinical studies. “Release hypothesis” proposed an intrinsic masticatory oculomotor neural circuit and this kind circuit, which, however, has been observed only in amphibian. On the other hand, congenital miswiring hypothesis has overwhelmed other interpretations. However, the same phenomenon visualized in MGS cases was unveiled in human subjects without any sign of congenital oculomotor disorder. To further study co-firing of the upper eyelid and jaw muscles, we applied non-invasive EMG recording of the upper eyelid and ipsilateral masseter muscle belly in nine healthy volunteers. LP activity was determined initially by looking upward and active retraction of upper eyelid with head fixed. Then, dual channel inputs from upper eyelid and masseter muscle was recorded during tooth occlusion motivated by isometric masseter muscle contraction without jaw and face moving. The EMG recorded from upper eyelid when the subjects retracted eyelid with head fixed exhibited the same pattern as that collected during tooth occlusion, but the pattern was completely different from EMG of active eye closure. This reflects tooth occlusion evoked LP activity. Then, simultaneous co-firing of the LP and masseter muscle was recorded simultaneously during tooth occlusion without jaw movement. Finally, the aforementioned co-firing was recorded when the subjects conducted rhythmic occlusion and synchronous EMG from both muscles was acquired. In conclusions, humans may also have an intrinsic masticatory oculomotor circuit and release hypothesis may apply, at least, to some cases of MGS.     

EEG and fMRI Coregistration to Investigate the Cortical Oscillatory Activities During Finger Movement

Electroencephalography combined with functional magnetic resonance imaging (EEG-fMRI) may be used to identify blood oxygenation level dependent (BOLD) signal changes associated with physiological and pathological EEG event. In this study we used EEG-fMRI to determine the possible correlation between topographical movement-related EEG changes in brain oscillatory activity recorded from EEG electrodes over the scalp and fMRI-BOLD cortical responses in motor areas during finger movement. Thirty-two channels of EEG were recorded in 9 subjects during eyes-open condition inside a 1.5 T magnetic resonance (MR) scanner using a MR-compatible EEG recording system. Off-line MRI artifact subtraction software was applied to obtain continuous EEG data during␣fMRI acquisition. For EEG data analysis we used the event-related-synchronization/desynchronization (ERS/ERD) approach to investigate where movement-related decreases in alpha and beta power are located. For image statistical analysis we used a general linear model (GLM) approach. There was a significant correlation between the positive-negative ratio of BOLD signal peaks and ERD values in the electrodes over the region of activation. We conclude that combined EEG-fMRI may be used to investigate movement-related oscillations of the human brain inside an MRI scanner and the movement-related changes in the EMG or EEG signals are useful to identify the brain activation sources responsible for BOLD-signal changes.     

Neurophysiological aspects of eye and eyelid movements during blinking in humans

The neural relationships between eyelid movements and eye movements during spontaneous, voluntary, and reflex blinking in a group of healthy subjects were examined. Electromyographic (EMG) recording of the orbicularis oculi (OO) muscles was performed using surface electrodes. Concurrently, horizontal and vertical eye positions were recorded by means of the double magnetic induction (DMI) ring method. In addition, movement of the upper eyelid was measured by a specially designed search coil, placed on the upper eyelid. The reflex blink was elicited electrically by supraorbital nerve stimulation either on the right or the left side. It is found that disconjugate oblique eye movements accompany spontaneous, voluntary as well as reflex blinking. Depending on the gaze position before blinking, the amplitude of horizontal and vertical components of the eye movement during blinking varies in a systematic way. With adduction and downward gaze the amplitude is minimal. With abduction the horizontal amplitude increases, whereas with upward gaze the vertical amplitude increases. Unilateral electrical supraorbital nerve stimulation at low currents elicits eye movements with a bilateral late component. At stimulus intensities approximately two to three times above the threshold, the early ipsilateral blink reflex response (R(1)) in the OO muscle can be observed together with an early ipsilateral eye movement component at a latency of approximately 15 ms. In addition, during the electrical blink reflex, early ipsilateral and late bilateral components can also be identified in the upper eyelid movement. In contrast to the late bilateral component of upper eyelid movement, the early ipsilateral component of upper eyelid movement appears to open the eye to a greater degree. This early ipsilateral component of upper eyelid movement occurs more or less simultaneously with the early eye movement component. It is suggested that both early ipsilateral movements following electrical stimulation do not have a central neural origin. Late components of the eye movements slightly precede the late components of the eyelid movement. Synchrony between late components of eyelid movements and eye movements as well as similarity of oblique eye movement components in different types of blinking suggest the existence of a premotor neural structure acting as a generator that coordinates impulses to different subnuclei of the oculomotor nucleus as well as the facial nerve nucleus during blinking independent from the ocular saccadic and/or vergence system. The profile and direction of the eye movement rotation during blinking gives support to the idea that it may be secondary to eyeball retraction; an extra cocontraction of the inferior and superior rectus muscle would be sufficient to explain both eye retraction and rotation in the horizontal vertical and torsional planes.     

Sleep and its homeostatic regulation in mice lacking the adenosine A1 receptor

Sleep deprivation (SD) increases extracellular adenosine levels in the basal forebrain, and pharmacological manipulations that increase extracellular adenosine in the same area promote sleep. As pharmacological evidence indicates that the effect is mediated through adenosine A1 receptors (A1R), we expected A1R knockout (KO) mice to have reduced rebound sleep after SD. Male homozygous A1R KO mice, wild-type (WT) mice, and heterozygotes (HET) from a mixed 129/C57BL background were implanted during anesthesia with electrodes for electroencephalography (EEG) and electromyography (EMG). After 1 week of recovery, they were allowed to adapt to recording leads for 2 weeks. EEG and EMG were recorded continuously. All genotypes had a pronounced diurnal sleep/wake rhythm after 2 weeks of adaptation. We then analyzed 24 h of baseline recording, 6 h of SD starting at light onset, and 42 h of recovery recording. Neither rapid eye movement sleep (REM sleep) nor non-REM sleep (NREMS) amounts differed significantly between the groups. SD for 6 h induced a strong NREMS rebound in all three groups. NREMS time and accumulated EEG delta power were equal in WT, HET and KO. Systemic administration of the selective A1R antagonist 8-cyclopentyltheophylline (8-CPT) inhibited sleep for 30 min in WT, whereas saline and 8-CPT both inhibited sleep in KO. We conclude that constitutional lack of adenosine A1R does not prevent the homeostatic regulation of sleep.     

Detection of visual stimuli in far periphery by rats: possible role of superior colliculus

Summary The cataleptic state induced by injection of the GABAmimetic drug muscimol into the rat's ventromedial thalamic nucleus (VM) was examined using an electromyographic (EMG) approach. Muscimol in doses up to 50 ng/0.5 l injected into the VM induced a tonic EMG activity in the gastrocnemius muscle which is considered to be a measure of limb rigidity. This tonic EMG activity was found to be dose-dependent, GABA specific and locus specific. By recording EMG signals from chronically implanted electrodes in awake, unrestrained rats it was shown that muscular reactions serving to maintain the animal's static equilibrium were intact in the state of VM induced catalepsy. However, animals were unable to initiate movements or locomotion even when they were forced by strong external stimuli. It was found that the animals' immobility was due to an inability to induce a phasic activation of their muscles whereas tonic activation still occurred. It is concluded that (1) the rat's VM is part of a neuronal chain conducting information relevant for the expression of limb rigidity, (2) the VM is involved in the central mechanisms responsible for the phasic activation of a set of muscles.On leave from: Department of Pharmacology, Medical School, Jaczewskiego 8, PL-20-090, Lublin, Poland     

Arousal episodes during sleep in the neonatal rat

Hippocampal EEG and neck EMG activity were recorded in restrained as well as in unrestrained rat pups following treatment with drugs which selectively suppress wakefulness and active sleep, respectively. Chloral hydrate did not affect active sleep but eliminated the bursts of coordinated total-body movements which were seen during sleep, especially under conditions of restraint. Chlorimipramine, in contrast, suppressed active sleep while sparing the coordinated total-body motility. It is concluded that these latter movements represent an episodic arousal phenomenon, against a background of quiet sleep, which becomes intensified under certain postural conditions.     

Low-noise cable and slip-ring assembly for recording of small-amplitude physiological signals in chronic animals

A method is described for the construction of a multichannel low-noise cable and counter-balanced slip-ring device utilising commercially available components. This apparatus was used in conjunction with a system for recording microvolt physiological signals in unrestrained animals, and resulted in a substantial reduction of movement artefact. Although this method was used for recording the electroencephalogram (e.e.g.) in cats with chronically implanted electrodes, it is readily adaptable to other biomedical studies requiring artefact-free recording conditions.     

Measurement of the extraocular spike potential during saccade countermanding

The stop signal task is used to investigate motor inhibition. Several groups have reported partial electromyogram (EMG) activation when subjects successfully withhold manual responses and have used this finding to define the nature of response inhibition properties in the spinal motor system. It is unknown whether subthreshold EMG activation from extraocular muscles can be detected in the saccadic response version of the stop signal task. The saccadic spike potential provides a way to examine extraocular EMG activation associated with eye movements in electroencephalogram (EEG) recordings. We used several techniques to isolate extraocular EMG activation from anterior electrode locations of EEG recorded from macaque monkeys. Robust EMG activation was present when eye movements were made, but no activation was detected when saccades were deemed canceled. This work highlights a key difference between the spinal motor system and the saccade system.     

Separation of electrocardiographic and encephalographic components based on signal averaging and wavelet shrinkage techniques

During ambulatory monitoring, it is often required to record the electroencephalogram (EEG) and the electrocardiogram (ECG) simultaneously. It would be ideal if both EEG and ECG can be obtained with one measurement. We introduce an algorithm combining the wavelet shrinkage and signal averaging techniques to extract the EEG and ECG components from an EEG lead signal to a noncephalic reference (NCR). The evaluation using simulation data and measured data showed that the normalized power spectrum unvaried in all frequency bands for the EEG components, and the sensitivity and specificity of R-wave detection for the ECG component were nearly 100%.     

Implantable electrical and mechanical interfaces with nerve and muscle

The past ten years have witnessed the introduction of several new methods for chronic recording of electrical activity in peripheral nerves, single nerve fibers and muscles, and for monitoring mechanical events correlated with muscular action. Although these methods were developed as research tools in the study of movements of unrestrained, intact animals, such implantable interfaces with nerve and muscle also promise to be of value in clinical applications; some novel clinical efforts are already being pursued. A review is given of various new techniques that may be clinically applicable and the issues of surgical constraints, quality of signal isolation, and long-term reliability of implantable devices, which ultimately determine the usefulness of each method, are discussed. Experimental devices reviewed include nerve cuff electrodes, floating single-unit electrodes, EMG electrodes, length gauges, and force gauges. General considerations for potential clinical applications are then given.     

Sleep in the domestic hen (Gallus domesticus)

Electrophysiological recordings were made of five closely observed hens, all permanently implanted with both EEG and EMG electrodes. Five behavioural postures were distinguished and percentages of wakefulness, sleep and presumably paradoxical sleep (PS) were determined during the third and sixth hour of the dark period. Substantial agreement was generally found between behaviour and sleep with the exception of sitting or standing motionless with at least one eye open. During two thirds of this behavioural posture, the EEG showed large amplitude slow waves undistinguishable from slow wave sleep. Characteristics of PS were determined: periods were short, whereas its percentage increased during the night. Furthermore, EMG atonia was never found. An all night recording was made, and delta activity (2-5 Hz) was filtered and plotted against time for three of the hens. A significant decrease in delta activity across the night was found. Differences and similarities between sleep in hens and in mammals are discussed. Although large similarities exist it is concluded that some properties of birds' sleep make it unique and are a challenge for further study.