S183 to a tumour. The other 33 abnormal images involved atrophic lesions (17 patients, 50%), congenital anomalies (9 patients, 26%), calcifications (4 patients, 12%) and vascular disturbances (3 patients, 9%). In 11 children (15.7%) infantile spasms were of the cryptogenic type and fifty nine (84.3%) were symptomatic in type. In 10% of the symptomatic patients CT-scan was the only positive investigation. The children with normal CT-scan, before spasms began, had a normal psychomotor development in a greater percentage (62.5%) as compared with those having abnormal CT-scan (38.2%). 1 to 3 years after the beginning of infantile spasms and treatment with ACTH, 62.5% of the children with normal CT-scan had a favourable developmental outcome as opposed to 20.8% with abnormal scan. An abnormal CT-scan is a sign of poor developmental outcome in children with infantile spasms.
and Wong, Epilepsia, 1984, 25: 705). The characteristic field presents with negativity over the centro-temporal area, and simultaneous positivity bifrontally. However, such foci are also seen in other disorders. Do they indicate a benign or 'functional' focus? Can they help predict prognosis and epileptogenicity of the discharge? Tracings containing a centro-temporal spike with this H D pattern were identified from EEGs performed in our laboratory over a 2 year period (over 4000 EEGs). Clinical information was obtained from referring physicians, emphasizing: past history; family history; seizures; medications: intelligence; school performance and neuropsyc hological, neurological and CT findings. Preliminary findings will be presented, with examples of scalp potential fields in selected cases using topographic mapping technique. The possible significance of such HD discharges will be discussed.
P32.04 M I D - T E M P O R A L SPIKES IN C H I L D H O O D EEGs AND T I l E H I P P O C A M P U S .
P32.06 LOCALISAT1ON OF EPILEPTIC SPIKES USING S P A T I O - T E M P O R A L M A P P I N G AND D I P O L E M O D E L L ING T E C H N I Q U E S .
(Sendal, Japan) In benign childhood epilepsy, the EEG often shows spikes in the mid-temporal regions, although there is no evidence of brain lesions in these regions. In this study, mid-temporal spikes are classified into 4 types from the viewpoint of scalp distribution, and it is hypothesized that these spikes might originate from the hippocampus and then spread to the scalp mainly by volume conduction. The subjects were 43 children: type 1 unilateral mid-temporal spikes (22 cases); type 2 bilateral synchronous spikes (6 cases); type 3 bilateral synchronous spikes with the two sides having opposite polarities (rare, 2 cases); and type 4 - bilateral asynchronous spikes (13 cases). Since in transverse sections of the hippocampus the pyramidal cells are arranged in the form of a 'C', scalp distributions might be explained as follows. If the axis of electrical dipoles of spikes in the hippocampus is oblique, the electrical potential will spread to the scalp unilaterally: if the axis is vertical, the potential will spread bilaterally; if the axis is horizontal, the two sides will have opposite poles. As to bilateral asynchronous spikes, the two hippocampi might be involved in generation of the spikes.
P32.05 C E N T R O - T E M P O R A L SPIKE FOCUS: T H E CLINICAL SIGNIFICANCE O F A D I P O L E FIELD.
Donna Gregory and P.K.H. Wong (Vancouver, Canada) The presence of a horizontal dipole (HD) field seen on scalp recordings in patients with Benign Rolandic Epilepsy of Childhood (BREC) has been described in recent literature (Gregory
G.W. Thickbroom, H.D. Davies
(Perth, W. Australia) Spatio-temporal mapping and dipole modelling techniques have been applied to study the scalp fields and sources of focal spikes in 10 epileptic subjects with temporal or frontal cortical foci. Sixteen channels of monopolar EEG were recorded from 10-20 system electrode sites with a balanced sterno-clavicular reference using a Grass EEG machine interfaced to a PDP 11/23 computer. The operator viewed a conventional bipolar EEG trace and triggered the computer to store 1 sec. epochs of interest on disk. Reference independent (source derivation) waveforms were computed off-line and colour-coded spatiotemporal maps of the spike and of immediate pre- and postspike events were generated at 4 msec intervals and were displayed on a Tektronix 4105 colour terminal (Thickbroom, Electroenceph. clin. Neurophysiol, 1984, 59: 425). Dipoles were modelled to give an origin and orientation in both the horizontal and saggital planes. Results were correlated with cranial CT and operative findings when available. Our findings indicate that the combination of spatio-temporal mapping and dipole modelling allows a greater degree of precision than conventional EEG in localising the source of epileptic discharges.