Morphologic characteristics of the epileptogenic brain tumours

$217 diagnosis, including those with petit mal, television epilepsy and a larger group with primary generalised - 'idiopathic' epilepsy. From those in these categories in the years 1980 to 1984, 509 in all, a w i n t e r / s u m m e r difference did not emerge, Indeed almost twice as many cases presented in the summer than winter. When another group for the same period with specific abnormal responses during photic stimulation were studied, the seasonal trend was similarly not marked. A retrospective study concerning the large photosensitive population previously studied in Birmingham (Jeavons and Harding, 1975) was re-assessed. The results of 18 patients who had received detailed study of photosensitivity during both winter and summer were analysed. Sixteen patients had been investigated whilst receiving Valproate at a consistent dosage on both occasions, producing a controlled series of 20 investigations in both summer and winter. No evidence could be obtained of a preponderance of photosensitivity within the same patients in winter.The photosensitive range was greater in summer in 6 patients, was consistent between summer and winter in 4 and was greater in winter in 10. Was the study of Danesi properly controlled?

P41.13 O N T O G E N E T 1 C A S P E C T S O F N O N S P E C I F I C HYP E R V E N T I L A T I O N EFFECT IN C H I L D R E N A N D ITS REL A T I O N T O D I A G N O S I S O F SEIZURES. K.-tt. Daute and H. Dietze (Jena, E. Germany) The hyperventilation effect (mean) was calculated, based on grading the effect (7 intensities) in 33,504 EEGs of 4 to 18 year old paediatric patients, with respect to age. The resulting points follow a decreasing 'logistic' function (r = 0.98). The high delta effects (Gibb's build-up) show plateau-like stepwise decrease according to other neuro-developmental criteria. Quantitative probability analysis of fixed parameter 'seizures' in 1,962 EEGs revealed that epilepsy is correlated strongly with high effects, indifferently with medium and negatively with slight or absent effects. Non-epileptic records are inversely correlated. Probabilities for each catamnestic result can be predicted depending on the grade of given hyperventilation effect, as percent intervals.

P41.14 M O R P H O L O G I C C H A R A C T E R I S T I C S OF T H E E P I L E P T O G E N 1 C BRAIN T U M O U R S . M. Cepreganov, P. Tofovic and M. Stojanov (Skopje, Jugoslavia) In a total of 554 brain tumours, 124 epileptogenic and 430 non-epileptogenic, a correlation has been made between morphologic and 'tomodensitometric' characteristics, and the following have been studied: the region, size and tumour density;

the secondary intra-tumoural changes; contrast retention; peritumoural oedema; displacement of the medial structures and obstructive hydrocephalus and the extent of tumour growth towards the adjacent tissue. The significant epileptogenic regions are the following: the temporal (36.3%), frontal (23.4%), and the parietal (33.3%). The other regions have either very small epileptogenicity or have none at all. The average size of the epileptogenic tumours was 27 cm 3 ( ± 5 cm3), while that of the nonepileptogenic oqes 21 cm 3. The hypodense tumours have above average epileptogenicity with 55.3%, and the hyperdense ones only 24.5%. The secondary intratumoural changes, particularly the presence of necrotic and cystic margins, haemorrhages and calcification in the tumour did not influence epileptogenicity at all. The contrast retention that indirectly points to the tumour vascularization, and the disturbance of the hemato-encephalic barrier, respectively, did not influence the epileptogenicity and the percentage of contrast retention was 65% in both the epileptogenic and the non-epileptogenic brain tumours. Peritumoural oedema did not show significant creation of the epileptogenic seizures, however: in the epileptogenic tumours its presence has been noticed in 73.4%, while in the non-epileptogenic ones in 35%. Displacement and obstructive hydrocephalus, which indirectly depends on the size of the brain tumour have not influenced epileptogenicity. Finally, tumours with 'infiltrative' growth showed significant epileptogenicity (73%) in relation to tumours with non-infiltrative growth (37%).

MOTOR CONTROL. P42.01 L O N G - T E R M M O D I F I C A T I O N OF SPINAL REFLEXES. J.R. Wolpaw, J.A. O'Keefe and R. Dowman (Albany, NY. USA) Primates can gradually change the size of the largely monosynaptic spinal stretch reflex without change in initial muscle length or background E M G activity when reward is contingent on size of reflex (Wolpaw et al., J. Neurophysiol. 1983, 50; 1296). Change develops, reverses and redevelops over months and persists for long periods. It is relatively specific to the agonist muscle and affects movement. While size can increase or decrease, depending on the reward contingency, decrease occurs faster and lasts longer. Current work shows that the H reflex is also capable of such change, suggesting that the site of change is the Ia fiber synapse on the alpha motoneuron. This newly-described phenomenon, long-term adaptive plasticity in spinal reflexes, is similar to changes occurring with normal development, certain prolonged athletic training, and a variety of suprasegmental lesions. In each case, chronic change in descending spinal cord activity has gradual and persistent