Non-invasive Electrophysiological Recordings Research Articles

Dynamic causal models of steady-state responses

In this paper, we describe a dynamic causal model (DCM) of steady-state responses in electrophysiological data that are summarised in terms of their cross-spectral density. These spectral data-features are generated by a biologically plausible, neural-mass model of coupled electromagnetic sources; where each source comprises three sub-populations. Under linearity and stationarity assumptions, the model's biophysical parameters (e.g., post-synaptic receptor density and time constants) prescribe the cross-spectral density of responses measured directly (e.g., local field potentials) or indirectly through some lead-field (e.g., electroencephalographic and magnetoencephalographic data). Inversion of the ensuing DCM provides conditional probabilities on the synaptic parameters of intrinsic and extrinsic connections in the underlying neuronal network. This means we can make inferences about synaptic physiology, as well as changes induced by pharmacological or behavioural manipulations, using the cross-spectral density of invasive or non-invasive electrophysiological recordings. In this paper, we focus on the form of the model, its inversion and validation using synthetic and real data. We conclude with an illustrative application to multi-channel local field potential data acquired during a learning experiment in mice.

Mean-Fields and Neural Masses

Mean-Fields and Neural Masses

The effects of combined caffeine and glucose drinks on attention in the human brain

The objective of this research was to measure the effects of energising drinks containing caffeine and glucose, upon mental activity during sustained selective attention. Non-invasive electrophysiological brain recordings were made during a behavioural study of selective attention in which participants received either energising or placebo drinks. We tested specifically whether energising drinks have significant effects upon behavioural measures of performance during a task requiring sustained visual selective attention, as well as on accompanying components of the event-related potential (ERPs) related to information processing in the brain. Forty healthy volunteers were blindly assigned to receive either the energising drink or a similar-tasting placebo drink. The behavioural task involved identifying predefined target stimulus among rapidly presented streams of peripheral visual stimuli, and making speeded motor responses to this stimulus. During task performance, accuracy, reaction times and ongoing brain activity were stored for analysis. The energising drink enhanced behavioural performance both in terms of accuracy and speed of reactions. The energising drink also had significant effects upon the event-related potentials. Effects started from the enhancement of the earliest components (C1/P1), reflecting early visual cortical processing in the energising-drink group relative to the placebo group over the contralateral scalp. The later N1, N2 and P3 components related to decision-making and responses were also modulated by the energising drink. Energising drinks containing caffeine and glucose can enhance behavioural performance during demanding tasks requiring selective attention. The behavioural benefits are coupled to direct effects upon neural information processing.

Auditory brainstem response (ABR), a noninvasive electrophysiological method for the study of hearing ability of fishes

Over the past 100+ years several methods have been used to study hearing ability of fish. Behavioral (psychophysical) methods including food reward, barrier crossing, and electrical shock conditioning are used to train fish to respond to sound. Invasive-type of electrophysiological methods include single unit and microphonics recordings. In 1996, my laboratory developed auditory brainstem response (ABR) recording technique, an electrophysiological far-field recording method, to record acoustically evoked brainstem potentials from fish. This noninvasive method overcomes the major limitations of traditional behavioral (prolonged training period; erratic behavioral response) and electrophysiological (invasive surgery) methods. The ABR recording can be achieved easily with assemblage of conventional electrophysiological devices with the aid of computer programs. Since the development of this noninvasive electrophysiological recording method, it has been widely adopted by many laboratories around the world to study fish hearing. The role of gasbladder in hearing enhancement, the ontogenetic development of hearing ability of embryo and larval fish, the impacts of noise exposure on threshold shifts, the effect of aging on hearing all have been understood with the use of ABR method. This quick pace of achievement cannot be obtained without the use of this noninvasive recording technique. [Work supported by NIH, NOHR, IMLS.]

Behavioral plasticity and central regeneration of locomotor reflexes in the freshwater oligochaete, Lumbriculus variegatus. I: Transection studies

Abstract. Access to the ventral nerve cord in living specimens of Lumbriculus variegatus, an aquatic oligochaete, is normally impossible because surgical invasion induces segmental autotomy (self‐fragmentation). We show here that nicotine is a powerful paralytic agent that reversibly immobilizes worms, blocks segmental autotomy, and allows experimental access to the nerve cord. Using nicotine‐treated worms, we transected the ventral nerve cord and used non‐invasive electrophysiological recordings and behavioral analyses to characterize the functional recovery of giant nerve fibers and other reflex pathways. Initially, after transection, medial giant fiber (MGF) and lateral giant fiber (LGF) spikes conducted up to, but not across, the transection site. Reestablishment of MGF and LGF through‐conduction across the transection site occurred as early as 10 h (usually by 20 h) after transection. Analyses of non‐giant‐mediated behavioral responses (i.e., helical swimming and body reversal) were also made following nerve cord transection. Immediately after transection, functional reorganization of touch‐evoked locomotor reflexes occurred, so that the two portions of the worm anterior and posterior to the transection site were independently capable of helical swimming and body reversal responses. Similar reorganization of responses occurred in amputated body fragments. Reversion back to the original whole‐body pattern of swimming and reversal occurred as early as 8 h after transection. Thus, functional restoration of the non‐giant central pathways appeared slightly faster than giant fiber pathways. The results demonstrate the remarkable plasticity of locomotor reflex behaviors immediately after nerve cord transection or segment amputation. They also demonstrate the exceptional speed and specificity of regeneration of the central pathways that mediate locomotor reflexes.

Assessing sublethal neurotoxicity effects in the freshwater oligochaete, Lumbriculus variegatus

The sublethal neurotoxic and behavioral effects of five chemicals (4-aminopyridine, cadmium chloride, carbofuran, chloroform and diazinon) were examined in the freshwater oligochaete, Lumbriculus variegatus (Family Lumbriculidae), following short-term exposure by immersion. Noninvasive electrophysiological recordings of touch-evoked medial giant nerve fiber (MGF) spikes were obtained, before and after exposure, using printed circuit board recording grids. Neurotoxic effects included substantial, and reversible, decreases in MGF conduction velocity following exposure to all chemicals, except CdCl 2. Reversible losses of MGF touch sensitivity occurred with exposure to chloroform and CdCl 2. Hypersensitivity of the MGF to touch, accompanied by high-frequency spike trains and rebound spikes, occurred with exposure to 4-aminopyridine. Our approach provides a rapid and sensitive means of detecting and differentiating sublethal neurotoxic effects, in vivo, in this cosmopolitan benthic oligochaete.

Cerebral Function Analyzing Monit Evoked Potentials as a Noninvasivc Detecting Cerebral Dysfunction in Acute Hepatic and Renal Failure Tr Intermittent Machine Hemofiltration

We monitored the effect of 7 intermittent machine hemofiltration treatments in 4 patients with fulminant hepatic failure who had progressed to grade IV coma and developed acute oliguric renal failure. Prior to treatment the processed EEG showed excess slow wave activity, and the latency of the later visual evoked potentials (N2 and P2) was delayed. Following treatment there was a further increase in both EEG slow wave activity and latency of the N1, N2, and P2 potentials. Intracranial pressure increased from a median of 8 mm Hg (2-12, range) to 14 (8-28) following treatment, p < 0.05. There was a correlation between intracranial pressure and all of the later visual evoked potentials, for N3 r = 0.71, for P1 r = 0.39, and P2 r = 0.74, all p < 0.05. Although there appeared to be a good correlation between intracranial pressure and the noninvasive electrophysiological recordings, there were major changes in intracranial pressure, cerebral perfusion pressure, and cerebrospinal fluid pH during the first hour of treatment, during which time there were no discernable changes in EEG or evoked potentials. In this study, non-invasive neurophysiological methods were not found to be reliable as invasive methods in assessing acute, minute-by-minute changes in cerebral metabolism but these methods may have a role in the longer term in assessing patient prognosis.

Morphallaxis in an aquatic oligochaete, Lumbriculus variegatus: Reorganization of escape reflexes in regenerating body fragments

We describe functional and anatomical correlates of the reorganization of giant nerve fiber-mediated escape reflexes in body fragments of an aquatic oligochaete, Lumbriculus variegatus, a species that reproduces asexually by fragmentation. Since fragments from any axial position always regenerate short heads (seven or eight segments long) and much longer tail sections, segments originating from posterior fragments become transposed along the longitudinal axis and acquire, by morphallaxis, features of escape reflex organization that conform to their new anterior position. Using noninvasive electrophysiological recordings we have quantified, on a day-to-day and a segment-by-segment basis, the reorganization that occurs in sensory field arrangements of the medial (MGF) and lateral (LGF) giant nerve fibers, as well as changes in giant fiber conduction velocity and morphometry. Our results show that (1) posterior fragments, originally subserved by the LGF sensory field gradually become subserved by the MGF sensory field; (2) appropriate increases in the ratio of MGF:LGF cross-sectional area, perimeter, and conduction velocity accompany the reorganization in giant fiber sensory fields; and (3) sensory field reorganization can be repeatedly reversed by additional amputations. These results demonstrate that the functional organization of escape reflexes is highly plastic and that morphallaxis may result from the counterbalance of morphogenic influences localized within the anterior and posterior ends of regenerating body fragments.

Non‐invasive electrophysiological monitoring: A sensitive method for detecting sublethal neurotoxicity in earthworms

AbstractEarthworms were exposed, by external surface contact, to three chemical pollutants: dieldrin (a known neurotoxicant), dimethyl phthalate and fluorene (a possible neurotoxicant). After 48 h of exposure, LC50 values were determined and compared with concentrations required for sublethal neurotoxic effects on giant nerve fiber conduction velocity and escape reflex function, as assessed by nonin vasive electrophysiological recordings. For dieldrin, sublethal decreases in giant fiber conduction velocity occurred at concentrations as low as 1.4 ppm, whereas much higher concentrations were required for lethality (48‐h LC50 = 8,100 ppm). Other sublethal effects of dieldrin included hyperresponsiveness of giant fibers, reduction in giant fiber‐mediated muscle potentials, tonic spasms of longitudinal shortening and ataxia. For fluorene, sublethal neurophysiological effects, including reduced conduction velocity and occasional “rebound” spiking of giant fibers, were evident at 100 and 250 ppm. By comparison, the 48‐h LC50 for fluorene was 360 ppm. No sublethal neurophysiological effects were evident following treatment with dimethyl phthalate; the 48‐h LC50 was 10,900 ppm. The results indicate that noninvasive electrophysiological recording of earthworm escape reflex function can be used as a sensitive means of detecting potential sublethal neurotoxic effects of pesticides and other environmental pollutants in these nontarget organisms.

In vivo neurotoxic effects of dieldrin on giant nerve fibers and escape reflex function in the earthworm, Eisenia foetida

Neurotoxicological effects of dieldrin were assessed in adult earthworms, Eisenia foetida, using noninvasive electrophysiological recordings of escape reflex activity. After 48 hr body surface exposure to aqueous suspensions of dieldrin, dose-dependent reductions in medial and lateral giant nerve fiber conduction velocities were seen within a concentration range of 1.4 to 288 ppm. At a high concentration (288 ppm) the decreases in velocity occurred in as little as 90 min, but at low concentrations decreases in velocity occurred much more gradually. Other physiological and behavioral effects of dieldrin treatment included (i) after-discharges of giant fibers following brief mechanical stimulation, (ii) spontaneous bursts of giant fiber spikes, (iii) reductions in the amplitude of giant fiber-mediated muscle potentials, (iv) tonic spasms involving end-to-end shortening and body stiffening, (v) ataxia, and (vi) reduction in body weight. Thus, the in vivo effects of dieldrin in earthworms are characterized by a diverse and complex set of physiological and behavioral symptoms. Possible mechanisms underlying these effects are discussed in relation to the generally accepted mode of dieldrin action on synaptic transmission.

Species specificity of giant nerve fiber conduction velocity in oligochaetes

Giant nerve fiber conduction velocities were studied using noninvasive electrophysiological recording techniques in adults from 12 species of oligochaetes, representing five different families. Two separate and stereotyped all-or-none response patterns to tactile stimulation (corresponding to medial and lateral giant fiber spike responses) were observed in all 12 species, suggesting that this functional dichotomy has been a conserved feature in the evolution of oligochaete escape reflexes. The results indicate that there is considerable species specificity with respect to medial and lateral giant fiber conduction velocities, which may derive from species differences in genetically determined limits in the radial growth of the giant fibers.

Electrophysiological correlates of rapid escape reflexes in intact earthworms, Eisenia foetida. II. Effects of food deprivation on the functional development of giant nerve fibers.

Noninvasive electrophysiological recording methods were used to study the effects of prolonged food deprivation on the postembryonic patterns of giant fiber growth, as indicated by age-dependent changes in giant fiber conduction velocity and diameter, in the earthworm, Eisenia foetida. In addition, giant fiber growth was compared to patterns of somatic growth, as indicated by increases in body weight. Within a wide range of food deprivation levels, normal age-dependent increases in conduction velocity and diameter occurred in spite of marked stunting of somatic growth. Stunting of giant fiber velocity and diameter occurred only during severe food deprivation, but giant fiber spikes and associated rapid escape responses were still readily evoked. The stunting effects of prolonged and severe food deprivation upon giant fiber conduction velocity and diameter were readily reversed by replenishing food. The results demonstrate the persistence of rapid escape reflex functioning, as well as the priority of giant fiber growth relative to somatic growth, during severe and prolonged food deprivation. As a consequence of the priority of giant fiber growth during limited food availability, giant fiber conduction velocity appears to be a more reliable predictor of animal age then body size.

Longitudinal variations in MGF-mediated giant motor neuron activity and rapid escape shortening in intact earthworms

1.1. Longitudinal variations in the activity of the segmentally arranged giant motor neuron (GMN1) pathways of the earthworm have been studied using non-invasive electrophysiological recording techniques.2.2. When two MGF spikes and their associated GMN1 spikes are closely spaced (e.g. GMN1 interspike interval 4–8 msec), there is a marked increase in the amplitude of the second GMNl-mediated muscle potential.3.3. Due to a marked longitudinal gradient, these increases in muscle potential amplitude are greater in anterior than in middle or posterior segments.4.4. The large increase in muscle potential amplitude in anterior segments is consistent with the observation that MGF-GMN1-mediated shortening in anterior segments is greater, occurs earlier, and requires fewer antecedent GMN1 spikes than shortening in more posterior segments.5.5. The observed longitudinal gradient in motor activity may represent a mechanism for focussing rapid escape withdrawal into anterior segments, which would be most vulnerable to attack when the animal is extended from its burrow.

Longitudinal variations in the efficacy of lateral giant fiber to giant motor neuron transmission in intact earthworms

1. 1. Non-invasive electrophysiological recording methods have been used to characterize segmental variations in transmission between the lateral giant fiber (LGF) and segmentally arranged giant motor neurons (GMN2) in earthworms. 2. 2. LGF-GMN2 transmission is most effective in the first 30 segments of the animal, where usually a pair or occasionally a single LGF spike is sufficient to trigger a GMN2 spike. 3. 3. The efficacy of LGF-GMN2 transmission diminished along an anterior to posterior gradient, with least effective transmission occurring between segments 91 and 120. 4. 4. When a pair of closely spaced LGF spikes is initiated in the posterior end facilitation of LGF conduction velocity causes a gradual reduction (up to 2 msec) in the LGF interspike interval as the spikes are conducted anteriorly. 5. 5. This reduction in LGF interspike interval, in combination with the marked longitudinal gradient in LGF-GMN2 transmission efficacy, tends to focus GMN2 firing and its associated motor response (longitudinal shortening) into anterior segments which are most vulnerable to attack by predators.