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Ever since Liepmann's original descriptions at the beginning of the century apraxia has usually been attributed to damage confined to the cerebral cortex and/or cortico-cortical connecting pathways. However, there have been suggestions that apraxia can be due to deep subcortical lesions, which raises the question as to whether damage to the basal ganglia or thalamus can cause apraxia. We therefore analysed 82 cases of such 'deep' apraxias reported in the literature. These reports consisted of a small number (n=9) of cases studied neuropathologically, and a much larger group (n=73) in which CT or MRI was used to identify the size and extent of the lesion. The reports were subdivided into (i) those with small isolated lesions which involved nuclei of the basal ganglia or thalamus only, and not extending to involve periventricular or peristriatal white matter; (ii) those with large lesions which involved two or more of the nuclei, or one or more of these deep structures plus damage to closely adjacent areas including the internal capsule, periventricular or peristriatal white matter; and (iii) lesions sparing basal ganglia and thalamus but involving adjacent white matter. The main conclusions to be drawn from this meta-analysis are that lesions confined to the basal ganglia (putamen, caudate nucleus and globus pallidus) rarely, if ever, cause apraxia. Lesions affecting the lenticular nucleus or putamen nearly always intruded into the adjacent lateral white matter to involve association fibres, in particular those of the superior longitudinal fasciculus and frontostriatal connections. Apraxia occurred with deep lesions of the basal ganglia apparently sparing white matter in only eight out of the 82 cases. Apraxia was most commonly seen when there were lesions in the lenticular nucleus or putamen (58 out of 72 cases) with additional involvement of capsular, and particularly of periventricular or peristriatal, white matter. Lesions of the globus pallidus (no cases) or caudate nucleus (three cases) rarely caused apraxia. The caudate lesions also had white matter involvement. Indeed, involvement of periventricular white matter alone caused apraxia. The vast majority of cases described with apraxia associated with deep lesions were in the left, dominant hemisphere. Ideomotor apraxia was described in most reports (72 out of 82 cases). Orofacial apraxia was less common (37 cases), usually with ideomotor apraxia. Ideational apraxia was rare (five cases), all with ideomotor apraxia. Apraxia was either bilateral or involved the left hand if there was a right hemiparesis, in those cases where descriptions were available. Lesions of the thalamus can sometimes cause apraxia (26 cases), even if there is no apparent involvement of white matter (12 cases). Small lesions confined to the thalamus can also sometimes cause apraxia (eight cases). The role of the thalamus in higher order motor control and apraxia remains to be determined. It is suggested that the term limb-kinetic apraxia should be retained to describe motor deficits in planning 'what to do', 'how to do it' and 'when to do it'; decisions which appear to involve activation of a complex distributed network of dorsolateral prefrontal cortex, supplementary motor areas, anterior cingulate regions and lateral premotor cortex. Such deficits need to be quantified. If they are present in patients with basal ganglia disease, over and above classical akinesia, bradykinesia and hypokinesia, then such patients could be said to exhibit limb-kinetic apraxia.

The disorder of autosomal dominant nocturnal frontal lobe epilepsy has recently been identified, and is now delineated in detail. A phenotypically homogeneous group of five families from Australia, Britain and Canada, containing 47 affected individuals, was studied. The largest family contained 25 affected individuals spanning six generations. This disorder is characterized by clusters of brief nocturnal motor seizures, with hyperkinetic or tonic manifestations. Subjects often experienced an aura, and remained aware throughout the attacks. Seizures occurred in clusters (mean eight attacks/night) typically as the individual dozed, or shortly before awakening. The epilepsy usually began in childhood, and persisted through adult life, with considerable intra-family variation in severity. Seizures were often misdiagnosed as benign nocturnal parasomnias, psychiatric and medical disorders. Interictal EEG studies were unhelpful. Ictal video-EEG studies showed that the attacks were partial seizures with frontal lobe seizure semiology. Neuro-imaging was normal. Carbamazepine monotherapy was frequently effective. This disorder showed autosomal dominant inheritance. Recognition of this entity is clinically important for diagnosis, appropriate therapy and genetic counselling. Moreover, this disorder now offers an opportunity to identify a gene for partial epilepsy.

Among 25 baboons, Papio papio, 2 consistently showed acute dystonic reactions, with mouthing, compulsive gnawing and limb and trunk dystonia, following the intravenous administration of neuroleptics and related drugs (haloperidol, 0-6-1-2 mg/kg; pimozide 0-5-2-5 mg/kg; chlorpromazine 5-25 mg/kg; metoclopramide 1-5-1-7 mg/kg; oxyperomide 0-25-1-0 mg/kg). The syndrome was not seen after thioridazine (3-7 mg/kg). The dystonic responses occurred within 1-2 h of drug injection and lasted for 2-24 h. They were abolished for 1-3 h within 1-2 min of the intravenous injection of acetylcholine antagonists (benztropine 0-2 mg/kg; hyoscine 0-02 mg/kg). Pre-treatment with a combination of reserpine (2 mg/kg) and alpha-methylparatyrosine (2 X 200 mg/kg) substantially reduced the dystonic response to haloperidol. A second larger dose of haloperidol (5 mg/kg), given 60-90 min after 0-5 mg/kg) initially reduced the intensity of the dystonic response, but after 29 min induced vomiting and generalized seizures in the idiosyncratic baboons. The hypothesis is advanced that the dystonic responses result from release of dopamine on to a sub-population of receptors in the striatum that are relatively insensitive to blockade by neuroleptics.

The clinical and electrophysiological findings in 2 cases of familial essential myoclonus are presented. The myoclonus was inherited apparently as an autosomal dominant trait, onset was in the first decade of life and the course was benign without the development of other significant neurological deficits. The electroencephalogram was unremarkable. The electromyographic appearance of the myoclonus was 50-100 ms complex bursts, usually occurring alternately in agonists and antagonists, similar to a normal ballistic movement. Muscles throughout the body were activated synchronously. In one of the cases myoclonus occurred at rest, but in both cases the myoclonus could be regularly produced by attempting a rapid movement. The myoclonic activity occurred simultaneously with the appropriate muscle activity which initiated the ballistic movement. It was as if the command to generate a ballistic movement overflowed into an excessive number of muscles. From a review of the literature it was concluded that this physiological mechanism was probably responsible for a definite sub-group of essential myoclonus. The relation of this type of myoclonus to other types of myoclonus and other involuntary movement disorders is discussed.