Search PubMed⌕ Search

Biomedical subjects

N A Shaw

Publications and source records attributed to N A Shaw.

At least 37 records · Page 2Linked to original sources
PubMed1992

A possible collicular component of the auditory evoked potential and its relationship to brainstem and cerebellar auditory potentials.

Auditory evoked potentials were recorded from the rat using skull screw electrodes inserted over the inferior colliculus and the cerebellum. In addition, brainstem auditory evoked potentials (BAEPs) were also recorded. The response recorded from over the inferior colliculus consisted of a slow positive potential with one of two possible peak latencies. The mean latency of the earlier potential was 5.6 ms and that of the later potential was 6.4 ms. A hypothetical generator for the first collicular potential is the termination of the lateral lemniscus in the ventrolateral inferior colliculus, while the later collicular potential could have its origins within the brachium of the inferior colliculus. None of the principal nor minor BAEP waves corresponded to either of the collicular responses. Nor did the trough of negativity between BAEP waves IV and V which is often thought to reflect activity generated within the midbrain. The potential recorded over the cerebellum also consisted of a slow positivity but with a slightly sharper contour than that of the collicular response. The mean latency of the cerebellar potential was 4.9 ms. As there was no temporal relationship between collicular and cerebellar potentials, the present study provided no support for the theory that cerebellar auditory potentials are artefactual and simply far field reflections of activity generated in the inferior colliculus. Judging by the timing of the BAEP waves, it is also concluded that the afferent volley most likely projects to the cerebellum via a collateral pathway branching off the caudal part of the lateral lemniscus.

Acoustics↗
PubMed1991

Cloning of high-affinity methionine transport genes from Salmonella typhimurium.

At least one of the genes encoding a methionine transport system in Salmonella typhimurium has been cloned on a 15 kbp fragment in the lambda 1059 vector, and the region responsible for the transport activity was subcloned in a set of plasmids with inserts ranging from 1.4 to 4.2 kbp in the multicopy plasmid pUC8. Two proteins of Mr 34 and 40 kDa were expressed from the larger inserts.

Biological Transport↗
PubMed1991

A comparison between electroencephalography and somatosensory evoked potentials for outcome prediction following severe head injury.

The value of somatosensory evoked potentials (SEPs) for the prediction of outcome following severe head injury (HI) is established. The role of the electroencephalogram (EEG) in this setting is uncertain. In this comparative study, SEPs and EEGs were recorded within 3 days of severe HI in 90 patients, and the results related to outcome at 6 months. Patients with an isoelectric EEG or an EEG with repeated isoelectric intervals died. Reactivity of the EEG to external stimulation tended to be associated with favorable outcome. Grading of the EEGs on the basis of frequency composition otherwise provided no prognostic information. The presence of SEP scalp potentials bilaterally predicted favorable outcome, particularly if the central conduction times were normal. Conversely, the absence of one of both scalp potentials was associated with unfavorable outcome. EEGs thus provided useful prognostic information in only a minority of patients. By comparison, SEPs allowed prediction of both favorable and unfavorable outcomes in a much larger number of patients, and were therefore prognostically superior.

Adolescent↗
PubMed1991

A possible thalamic component of the auditory evoked potential in the rat.

An attempt is described to identify a thalamic component of the auditory evoked potential in the rat. Auditory potentials were recorded simultaneously from skull locations over the thalamus and the primary auditory cortex. From over the thalamus a slow positive response was recorded with a mean peak latency of 7.3 ms. This preceded the primary cortical response by 1.2 ms. It is concluded that this potential is a more likely candidate for a thalamic response than either a late high frequency component of the brainstem auditory evoked potential or else one of the early components of the middle latency auditory evoked potential.

Animals↗
PubMed1990

Central auditory conduction time in the rat.

Central conduction time is the time for an afferent volley to traverse the central pathways of a sensory system. In the present study, central auditory conduction time (CACT) was calculated for the rat, the first such formal measurement in any animal. Brainstem auditory evoked potentials (BAEPs) were recorded simultaneously with the primary response of the auditory cortex (P1). The latency of wave II of the BAEP, which arises in the cochlear nucleus, was subtracted from that of P1. This yielded a mean CACT of 6.6 ms. The results confirm a previous theoretical estimate that CACT in the rat is at least twice as long as central somatosensory conduction time.

Animals↗
PubMed1990

The effects of chloralose on the brainstem auditory evoked potential of the rat.

The effects of alpha-chloralose were examined on the brainstem auditory evoked potential of the rat. Subjects were given one of four different doses of chloralose. These were a sedative dose (50 mg/kg), an anaesthetic dose (100 mg/kg), a usually fatal dose (150 mg/kg) or an invariably fatal dose (200 mg/kg). Recordings were made 60 min later. There was no evidence of any dose-dependent increase or decrease in the amplitudes of the four principal components (waves I, II, III and IV) of the brainstem auditory potential. There were only minor dose-dependent increases in latency. These were less than 0.1 msec for waves I, II and III and just over 0.1 msec for wave IV. Wave IV was the component which was most sensitive to chloralose, although this was apparent only at a large dose. In general, the latencies showed little or no difference from those recorded previously from awake animals. The results are discussed in relation to a series of experiments, where animals were initially immobilized with chloralose in order to study the effects of a variety of pharmacological agents on the brainstem auditory potential.

Animals↗
PubMed1990

Early prediction of outcome from cerebral trauma by somatosensory evoked potentials.

The prognostic value of short-latency somatosensory evoked potentials (SEP) during the first 4 days after severe head injury was studied in a group of 100 ICU patients. There was a strong association between the presence of bilateral cortical potentials and a good recovery or moderate disability 6 months after injury. In contrast, the bilateral or unilateral absence of cortical potential was associated with severe disability, persistent vegetative state, or death in a high percentage of patients. A reliable prediction of outcomes was obtained from SEP recorded within 24 h of head injury. Predictive accuracy was not influenced by the time of recording or cumulative analysis of consecutive daily SEP over the first 4 days after injury. Short-latency SEP can provide a reliable and accurate prognosis for sedated and curarized patients, and can have an important role in the management and triage of patients with severe head injury who are undergoing intensive therapy.

Adolescent↗
PubMed1989

Epileptiform discharges in presence of continuous background activity in anoxic coma.

The EEGs of a group of patients in anoxic coma following cardiorespiratory arrest were retrospectively studied. Twelve of 70 patients had at least one EEG recorded during the acute period which consisted of epileptiform discharges in the presence of continuous diffuse background activity. Nine of the patients died while three made a generally favorable recovery. The analysis confirms the prediction of a recent revision of EEG grades in coma that this particular pattern of activity is of uncertain prognostic significance. This is in contrast to the occurrence of epileptiform discharges during discontinuous "burst suppression" activity which generally indicates a fatal outcome.

Aged↗
PubMed1988

Origin of reprint requests.

One thousand consecutive reprint requests were classified according to their countries of origin. One third came from the United States of America and over 70% originated in six countries (USA, Czechoslovakia, France, West and East Germany and Canada). When reprint requests were adjusted for population size, a different order became apparent with Czechoslovakia requesting proportionally the most, followed by Israel, East Germany, Canada, Switzerland and Belgium. Approximately half of the reprint requests came from European countries with the overall rates for western and eastern European nations being similar. There were comparatively few requests received from Third World nations. The analysis questions several of the reasons commonly given for honouring reprint requests.

Humans↗
PubMed1988

Effect of electroconvulsive shock on the slow components of the brain stem auditory evoked potential.

The effects of electroconvulsive shock on the slow components of the brain stem auditory evoked potential were investigated in the rat during the ictal and the immediate postictal periods. Shock did not significantly alter any aspect of the slow positive-negative complex which underlies the high-frequency waves of the brain stem auditory evoked potential. However, a succeeding potential of probable cortical origin was markedly reduced in amplitude and its peak latency was temporarily increased.

Animals↗
PubMed1988

Somatosensory evoked potentials following severe head injury: loss of the thalamic potential with brain death.

The thalamic component (P17) of the short-latency somatosensory evoked potential (SEP) was assessed to determine its usefulness in patients with severe head injury. Subjects were a group of patients admitted to the Auckland Hospital Critical Care Unit who subsequently died from head injury. In all instances where brain death was unequivocally established and a SEP recording made in close temporal proximity to the time of brain death the P17 potential was absent. When there was evidence of continuing brainstem activity and particularly where prolonged survival occurred following the last SEP recording the P17 potential remained intact bilaterally. This study shows that the presence or absence of the thalamic component of the short-latency SEP provides a reliable electrophysiological measure of brainstem function in patients where brain death has been suspected.

Adolescent↗
PubMed1988

Disruption of conditioned taste aversion: evidence that ECS weakens the gustatory engram.

Two experiments are reported concerning the neural substrate of conditioned taste aversion (CTA) and the amnesic mechanisms involved when such learning is disrupted by electroconvulsive shock (ECS). Subjects were adult male rats. In the first experiment it is demonstrated that an aversion established to a 2.5% sucrose solution can simulate the learning loss reported in earlier studies which was caused by interpolating ECS between tasting and illness when the aversion was established using a 10% sucrose cue. It is concluded that if ECS acts to disrupt the memory of the taste cue, it possibly reduces it to only about one-quarter of its original strength, a substantial deficit not readily apparent simply from the degree of aversion displayed. In the second experiment, CTAs were established using either a 2.5% sucrose cue or a 10% cue with ECS interpolated during the taste-illness interval. Animals in the two groups were subsequently confronted with a range of sucrose stimuli and their respective aversions were compared. Near identical responses were observed under all conditions tested. These findings are consistent with the theory that ECS disrupts CTA by weakening the gustatory engram.

Amnesia↗
PubMed1988

Interside amplitude asymmetries in the median nerve somatosensory evoked potential: normative data.

Short latency median nerve somatosensory evoked potentials (SEPs) were recorded from a group of 31 adults in order to establish the boundaries between normal and abnormal interside amplitude asymmetries. The potentials studied were the cervical SEP (N13) and the primary cortical response (N20). In order to more accurately analyse and compare intersubject data, the amplitude of the lesser potential was expressed as a percentage of the greater potential. The limit for normality was defined as 1 SD (of the mean amplitude asymmetry) below the lowest individual value observed among normal subjects. It is concluded that if a cervical potential from one side is no more than 60% of the potential from the other side, then this represents a significantly abnormal amplitude asymmetry. In contrast, a cortical potential must have an amplitude which is less than 36% of the larger potential in order to be considered significantly abnormal.

Adolescent↗
PubMed1988

Far field correlates of thalamic activity in cortical and cervical somatosensory evoked potentials.

Median nerve cortical and cervical somatosensory evoked potentials (SEPs) were recorded from a group of normal adults in order to study far field reflections of thalamic activity. In the cortical SEP, the primary response (N20) was preceded by two inflections (N16 and N18). It is shown that these two potentials bear a close temporal relationship to a positive trough on the downward slope of the principal negativity (N13) in the cervical SEP. This potential, which is often bifurcated into two subcomponents, is labeled P17 and it has previously been suggested that it originates in or near the thalamus. The coincidence between the P17 complex and N16 and N18 inflections is consistent with the hypothesis that all three responses are generated in either the thalamic relay nucleus or the thalamo-cortical radiations. Possible clinical applications of recording far field thalamic potentials are discussed.

Adolescent↗
PubMed1987

Effects of low pass filtering on the brainstem auditory evoked potential in the rat.

The effects of low pass filtering on the brainstem auditory evoked potential (BAEP) were studied in the adult male rat. The bandpass of the recording system was progressively widened while the cut-off frequency of the high pass filter remained constant at 3.2 Hz. When the high frequency cut-off was 320 Hz or less, the principal waveform recorded in response to a click stimulus was a slow positive-negative complex. As the high frequency setting was raised from 800 Hz to 3.2 kHz, the slow components of the brainstem were replaced by four fast BAEP waves (I, II, III and IV). As the bandpass widened there was an increase in amplitude and a decrease in the absolute latency of all four fast waves in the order of 0.1 ms although the wave I-IV interpeak latency remained unaffected. The results confirm that the high frequency components of the BAEP are underlain by a slow positivity of uncertain origin followed by a slow negativity which probably arises within the inferior colliculus.

Animals↗
PubMed1987

Intersession stability of somatosensory evoked potentials.

Upper and lower limb nerve somatosensory evoked potentials (SEPs) were recorded from a group of normal adults in order to assess their intersession stability. Median, peroneal and sural nerve SEPs were recorded from each subject on 3 successive occasions at weekly intervals. For median nerve SEPs, the intrinsic variability was more pronounced for interpeak latencies (N9-N20, N13-N20) than for the latencies of individual components. Their inherent fluctuation was not, however, notably greater for the primary cortical response (N20) than for the more caudally generated components (N9 and N13). These relationships were not so apparent for lower limb SEPs where intersession variability was markedly greater overall than for upper limb SEPs.

Adolescent↗