D. S. Dinner

Extraoperative cortical functional localization in patients with epilepsy

Functional localization prior to cortical resections for intractable seizures has usually been performed in the operating room in awake patients. Chronically placed subdural electrodes offer the possibility of performing such testing outside of the operating room and without the unavoidable stresses and time limitations of the surgical setting. The use of the technique is reviewed.

Objective criteria for reporting language dominance by intracarotid amobarbital procedure

We propose a standardized method for reporting language lateralization by intracarotid amobarbital procedure (IAP). We retrospectively reviewed 165 IAPs, and classified language lateralization as left, right, or bilateral by three different methods, all based on the duration of speech arrest following each injection: absolute duration, side-to-side difference, and a laterality index defined as (L-R/L+R). Cutoff values were obtained by studying a pure subgroup of left hemisphere dominant right-handed subjects. In 142 patients (86%), the classification remained unchanged among all three methods: left in 112 (79%), right in 19 (13%), and bilateral in 11 (8%). In the other 23 patients (14%), language classification varied among the three criteria used. The change of category was never between left and right, and always involved bilateral language. Thus, this index may be helpful in standardizing and comparing IAP results from different series.

Critical Analysis of the Methods Used to Identify Generator Sources of Evoked Potential (EP) Peaks

Optimal use of evoked potentials (EP) for clinical studies requires a good understanding of its generator sources. Numerous methodologies, many of them interrelated and all with significant limitations, have been used to define the generators of evoked potential peaks. In this chapter, we will discuss and analyze critically these different approaches.

Dystonic posturing in temporal lobe seizures

ple daily episodes of dystonic and choreoathetotic posturing. His movements began with his rubbing his right first and second digits together, followed by extension of the wrist, flexion of the elbow, and abduction of the shoulder, occasionally followed by head dropping. The movements lasted for seconds and could be precipitated by activity of the right arm. Birth history and early developmental motor milestones were normal. However, his language never properly developed. Physical examination revealed decreased hearing, and dressing and constructional apraxias. He was hypotonic with bilateral Hoffman and Babinski signs. Laboratory investigation, including CT and MRI, were normal. Several clinical seizures were recorded on a surface EEG with double density electrodes over the vertex (figure). The EEG study demonstrated interictal epileptiform activity between Cz and C1, and bursts of high-frequency epileptiform activity near Cz coincident with the patients right hand movement and head dropping. The surface potential pattern of this discharge was suggestive of ictal activity arising in the SMA contralateral to the involved extremity. To support their contention that the movements were mediated by striatal involvement, Kotagal et a1 cited anatomic evidence for projections from the hippocampus and amygdala to these structures. But these pathways project to the ventral striatum and are probably not related to the motor functions of the basal ganglia.2 However, there are connections between the temporal and frontal lobes, including direct projections from the amygdala to the SMA.S The SMA, in turn, has extensive connections with the striatum that are intimately involved in motor function.* The possible spread of ictal activity from temporal lobe to frontal lobe was not specifically monitored in Kotagals patients, since their intracranial EEGs (subdural grids) did not sample activity from the mesial frontal and cingulate areas. Furthermore, it is well known that stimulation-6 and ictal discharge4.6.7 from the SMA or cingulate gym provoke contralateral dystonic and choreoathetotic posturing. We suggest that dystonic posturing in CPS of temporal lobe origin likely reflects spread of ictal discharge to the ipsilateral mesial frontal lobe. Consequently, this area should be carefully studied in patients with such behaviors prior to concluding spread to the basal ganglia.

Technical Aspects of Surgical Monitoring Using Evoked Potentials

In our view the main objective during surgical monitoring is to record a clearly identifiable and highly reproducible response proximal to the surgical site. If a response alteration occurs it becomes important to know whether that alteration is due to an intraoperative mishap or is due to a technical problem unrelated to a surgical injury. For this reason it is important that the stimulation and recording methodologies are sufficient to result in reproducible and reliable responses. There is probably no single optimal technique for achieving this. Rather optimal results are obtained by adequate attention to many details (2, 5, 8).

Clinical Use of Evoked Potentials: A Review

The use of evoked potentials has become widespread in the past ten years. Evoked potentials have probably been obtained in patients with virtually all neurologic diseases. Much has been learned about proper techniques, and the neuropathways involved. Recently, several articles have discussed the use and abuse of evoked potentials in clinical practice [1,2,3,4].