The normal human audiogenic startle reflex is defined from a review of the literature, substantiated by a current investigation of normal subjects, and clarified pathophysiologically by a discussion of animal experimentation. The basic information is used to evaluate critically a variety of syndromes loosely termed 'startle' in the past. A new classification of startle syndromes is proposed.

SUMMARY A group of patients with myoclonus is described whose jerks are preceded by a bilaterally synchronous, frontocentrally predominant, negative cerebral potential in the EEG. This potential may be a slow wave with variable timing in relation to EMG bursts, and in this circumstance the muscle jerks are usually small amplitude and multifocal ("minipolymyoclonus"). The cerebral negativity can also be shorter in duration and time-locked to limb jerks, which are larger in amplitude and more widespread. We propose that the physiology of this distinct form of myoclonus is similar to that of primary generalised epilepsy.Myoclonus has been recognised in association with bilaterally synchronous discharges as recorded by scalp EEG. These paroxysmal discharges may assume a variety of forms: the regular 3 Hz spikewave activity of classic petit mal;' atypical, slower spike-wave paroxysms;23 diffuse spiking, spikewave, or polyspike wave as seen in myoclonic epilepsies or numerous encephalopathies;4 5 generalised, individual small amplitude " spikes" ;6 rapid 30 Hz central sinusoidal rhythms;5 or the more continuous rhythmic delta activity of a generalised cerebral disturbance.7 Recently, the categorisation of myoclonus into electrophysiological types68-12 has been facilitated by computerised methodology involving jerk-locked averaging of EEG data.'3 We now report a series of patients whose myoclonus was associated with a bilaterally synchronous electrocerebral event. form"-and the other in the well-described setting of Trisomy 21 (Down's syndrome).'6'8 The ninth patient was a 14-year-old girl with a familial progressive myoclonic epilepsy. The tenth patient had a degenerative disease of unknown nature. The last patient had typical petit mal epilepsy with 3 Hz spike and wave paroxysms on EEG and a strong family history. All patients were taking at least one anticonvulsant agent. MethodsEMG was recorded with pairs of surface electrodes placed longitudinally, 2-3 cm apart, over the mid-portion of the muscle. EEG was recorded with a Grass Model-8 electroencephalograph in referential linkage to ipsilateral ears with gold cup electrodes positioned in accordance with the 10-20 system (fig 1); the frequency response range was 1 to 35 or 70 Hz. The electrical signals were amplified and led to a PDP-11 computer which collected and sometimes averaged the data. Four to sixteen simultaneous data channels were employed. Computer collection was triggered by an event in one of the channels (using a Schmidt trigger pulse); events before and after the trigger could be recorded. The sensitivity of the trigger was set so that a trigger occurred only with definite jerks and not with occasional low level background EMG activity; by doing this, small jerks would not trigger a collection. Topographic analysis of 16-channel EEG data was carried out with computer programs previously described."9 506

The sensitivity and specificity of nerve conduction studies (NCS's) and electromyography (EMG) for the diagnosis of carpal tunnel syndrome (CTS) were evaluated by a critical review of the literature. With a search of the medical literature in English through May 1991, 165 articles were identified and reviewed on the basis of six criteria of scientific methodology. The findings of 11 articles that met all six criteria and the results of 48 additional studies that met four or five criteria are presented. We concluded that median sensory and motor NCS's are valid and reproducible clinical laboratory studies that confirm a clinical diagnosis of CTS with a high degree of sensitivity and specificity. Clinical practice recommendations are made based on a comparison of the sensitivities of the several different median nerve conduction study (NCS) techniques.

Ten patients with clinically diagnosed Alzheimer's disease, including three cases of trisomy 21 (Down's syndrome), developed a chronic myoclonic disorder. The technique of jerk-locked averaging of EEG activity was used to analyze the myoclonus. Seven subjects demonstrated a focal, contralateral central, negative cerebral potential antecedent to the myoclonic jerks. This EEG event differs from that previously reported to be associated with the myoclonus of subacute spongiform encephalopathy (Creutzfeldt-Jakob disease).