Computer-aided quantification of EEG spike and sharp wave characteristics.

This work presents data from detailed, computer-aided analysis of pertinent electrographic characteristics of well-defined EEG spikes and sharp waves. The data show morphological differences between spikes obtained from different subjects, spikes from different electrode montages, as well as between monophasic and biphasic spikes, and between spikes and sharp waves.

Electrocerebral activity only in response to stimulation and only at the vertex electrode.

This patient sustained a severe infarction, and an EEG carried out with accepted criteria by the American EEG Society ws consistent with electrocerebral inactivity. A repeat record demonstrated that activity was apparent mainly in a single electrode after stimulation. In this case, it was the vertex electrode that was active. The rest of the electrodes were inactive with the patient at rest and reflected little or no activity in response to stimulation. In this case at least, the persistence of EEG activity after stimulation had no prognostically favorable value in that the patient died.

Reversal of electrical sign in the occipital area: physiological or montage artifact.

The cases illustrate situations in which there is a polarity difference between the anterior and posterior regions resulting from the montage rather than actual physiological differences. The major most easily missed problems arise from diffuse slow waves, but a more easily recognized example of reversed or unexpected apparent polarity from a 14 and 6 per second positive spike burst is reviewed. Problems usually occur when waves in question have a wide distribution and provoke larger voltages in input 2 than in input 1 in some channels. The technologist needs to be aware of the potential problems. When they occur, a variety of montages including montages with a reference outside the involved area and possibly a non-cephalic reference can be employed to clarify the situation. A high index of suspicion, astute technologists and suspicious electroencephalographers are necessary to prevent misidentification of these wave forms as physiological in origin.

Persistence of EEG activity with prolonged induced hyperthermic fever.

Ten instances of deliberate systemic temperature elevation in the 41.5 degrees C to 42.2 degrees C range have been evaluated electroencephalographically, demonstrating decrease in predominant frequency and voltage. Persistence of electro-cerebral activity suggests that previous reports of electro-cerebral inactivity with elevated temperatures reflect indirect serious effects due to cardiovascular compromise with cerebral ischemia, rather than to a direct temperature-related loss of CNS electrical activity.