Electrical activity of subcortical areas in epilepsy

Abstract

The electrical activity of the cortex and subcortex were studied in 22 patients with epilepsy by means of scalp electrodes and a multi-electrode needle which was placed in the depths of the brain with the aid of a stereotaxic instrument. The instrument was designed for man and coordinate measurements were obtained by studies on brains fixed in situ. In the present operative series the position of the needle was checked by pneumoencephalography at the end of the recording. Analysis of records from the scalp and depths of the brain lead to the following conclusions: 1. 1. The cortex and sub-cortex in epileptic patients display comparable normal and abnormal activity. 2. 2. Like the cortex, however, various areas of the sub-cortex may show entirely independent abnormal activity. 3. 3. During the induction of pentathol anesthesia 20 to 30 per second activity appeared first and remained most prominent in outer subcortical leads and showed least in leads from the central grey mass. 4. 4. Isolated seizure discharges from the cortex are common, whereas they are rare in the subcortx. The fact that they do occur is important, because they may account for therapeutic failure in some cases where a cortical focus is ablated. 5. 5. No case was found in which seizure discharges in or around the medial thalamus could be interpreted as initiating 3 per second wave-and-spike discharges of the petit mal type. 6. 6. Primary and secondary cortical discharges have a negative sign when referred to a relatively indifferent area. An incoming volley from a distant area is registered as a positive disturbance if referred to an indifferent region. 7. 7. Electrical sign has localizing value in electroencephalography: Negativity indicates a local disturbance; positivity indicates a distant disturbance.