Auditory brain-stem responses in perinatal disorders

S36 of the fingers with identification of specific subcortical and cortical components. To assess cognition-related potentials, ‘exogenous obligatory’ responses recorded under ‘neutral’ conditions must be validated. Control profiles should be neither increased by unwanted cognitive (preconscious or conscious) commitment of the subject, nor decreased by refractoriness or habituation effects. On this basis, the somatosensory P30, P40, PlOO and N140 cognition-related components are analyzed with scatter displays, electronic subtraction of exogenous components, bit-mapping, and quantitative assessment of scalp topography with Z and DF estimators. Early cognitive components are shown to reflect attention-related ‘priming’ of neural generators in receiving somatosensory cortex. These can he observed in target signals, but also in signals that are under surveillance. Bit-mapped data on cognitive PlOO and N140 identify several distinct generators in posterior parietal and prefrontal cortex which reflect the parallel and serial processing mechanisms involved.

AUDITORY BRAIN-STEM RESPONSES DISORDERS. P.A. Despland, C. Gander (University

Hospital,

IN PERINATAL

and S. Winstanley

Lausanne,

Switzerland)

The auditory brain-stem responses (ABR) can provide clinically useful electrophysiological data on the auditory and neurological status of both premature and young babies. ABR as a tool for detecting transient or permanent audiological or neurological problems will be demonstrated in our study of more than 300 babies recorded in an ICU. A study of different risk factors presumes that any one of them may be the main cause of an audiological or neurological disorder. The apparent recovery of ABR on retest needs a valid procedure at the beginning, before we can assume the reversibility of some dysfunction of the inner ear and brain-stem structures in different disorders. According to our clinical data. the ABR seems a practical and realistic way to identify a very large percentage of babies with hearing and neurological disorders. ABR plays a crucial role in our ability to identify and treat those babies who need to be fitted with hearing aids during the first year of life. Even if in some perinatal disorders ABR can be less specific for a neurological problem, we are convinced that when properly used by skilled professionals it will almost never fail to supply information crucial for the early diagnosis and rational treatment of the hard-of-hearing infant,

ELECTRICALLY ELICITED THENAR REFLEXES: PHYSIOLOGICAL PROPERTIES AND NORMATIVE DATA. G. Dewchl and C.H. Liicking (Freiburg

University,

Reflexes of thenar nerve at threshold

Freiburg,

normal subjects (n = 52). All subjects exhibit the spinal Hoffmann-reflex (HR. mean latency +SD: 28.6+2:1 msec) and a subsequent long-latency reflex (LLR II. 50.3+3.0 msec). An additional LLR J (40.7 F 2.4 msec) or LLR III (75.1 i 2.8 msec) of low amplitude was found in I?%, or 7%. respectively. J‘ollowing stimulation of the radial superficial nerve only the LLR can be demonstrated. The individual reflex pattern is stable in long-term follow-up. The amplitudes of the HR and LLR JJ undergo significant decrease with increasing age. The LLR II is elicited by fast-conducting muscle and cutaneous afferents. Its saturation characteristic parallels that of the cortical somatosensory evoked potential following median nerve stimulation and differs from the saturation curve of the HR. We conclude that increased HR or LLR J amplitude, decreased amplitude or absence of LLR II or an increase of LLR II latency are abnormal findings of different significance. Physiological as well as pathophysiological investigations provide evidence for a transcortical reflex pathway, at least for the LLR II.

F.R.G.)

muscles following stimulation of the median for motor fibres have been standardized in

EEG IN THE STUDY ORGANIC SOLVENTS.

OF WORKERS

A. W De Weerd, E.J. Jonkman, huizen and J. Hooisma (Westeinde

Hospital,

The Hague,

D.C.J.

EXPOSED

Poortvliet,

TO

R.J. Veld-

The Netherlands)

In this study of the long-term effects of organic solvents, five groups were evaluated: young house painters (YP) (N = 40, mean age 37 years); young construction workers (YC) (N = 49, 37 years); elderly house painters (OP) (N = 41, 64 years); elderly construction workers (OC) (N= 37, 63 years) and normal subjects (NS) (N = 100, age range 20-70 years). All 267 subjects underwent an EEG which was assessed traditionally and analysed further for the peak frequency in the alpha range in the derivation 01-Cz and the mean frequencies in all bands at all locations. For the final step in the quantification of the EEG (qEEG) the ‘Neurometrics’ method (John et al., 1986) was chosen. In addition to the (q)EEG. visual evoked potentials (VEPs) and clinical and neuropsychological parameters were studied. The latter were essentially similar for the groups YP, YC, OP and OC, except for an excess of subjective symptoms in the painters’ group as revealed by a questionnaire. For the VEP study, see Jonkman et al., this meeting. In comparison to the normal subjects, 32-35% of all other EEGs were abnormal, even in the groups of young subjects. This was found with all forms of analysis of the EEG, with the exception of the peak detection method, which revealed no group abnormalities. The comparison of the YP and OP versus the YC and OC groups, which was the most important part of the study, revealed no significant differences. The results suggest some influence on cerebral function of long-term construction work and painting, but demonstrate no differences of these effects between the groups.