Kenneth A. Kooi

VISUAL EVOKED RESPONSES IN MAN: NORMATIVE DATA.

The fundamental importance of the characteristics of the cerebral electrical response to a simple pulse of light in man is evidenced by the number of workers who have provided information about its features from conventional recordings. Detailed description awaited the development of more powerful analytical tools. With the recognition of the usefulness of photographic superimposition, correlational analysis, and summation techniques (Dawson, 1947; Brazier and Casby, 1951, 1952; Dawson, 1954; Barlow and Brazier, 1954; Brazier and Barlow, 1956), the way was opened for a new phase in the examination of the complexities of cerebral organization. The major features of the visual evoked response have now been outlined by CigLnek, Cobb, Dawson and others. Studies which have included an analysis of latency and polarity of individual components of the response are listed in TABLE 1. The present study was designed to furnish additional information about response morphology, particularly as it might vary in relation to recording site, with the hope that it might lead to an increase in the clinical application of the technique. Also, a preliminary survey of possible relationships between major features of the response and such normal variables as age, eye color, refractive error, color blindness, pupil size, subjective estimate of light intensity, prior nights sleep, alpha frequency, alpha amplitude, and alpha persistence was undertaken.

Polarities and field configurations of the vertex components of the human auditory evoked response: a reinterpretation.

Abstract The cephalic spatial distributions and phase relationships of the late components, N 1 and P 2 , of the auditory evoked response, elicited by repetitive moderate-intensity tone pips, were assessed in man with a non-cephalic reference. There was no evidence of a polarity reversal at any site on the head, failing to confirm Vaughan and Ritters (1970) sylvian phase reversal hypothesis.

Electrophysiological findings in cortical blindness. Report of a case

Abstract Spontaneous cerebral activity and visual evoked responses have been described in a patient with post-traumatic cortical blindness who was studied over a period of 4 weeks. The resting occipital pattern was extremely small in amplitude but composed of frequencies largely within the normal alpha range. No evidence of light-induced alpha blocking could be detected. Averaged evoked responses derived from leads placed over the occipital poles were abnormal, in that they were rudimentary and inconsistent, none of the normal initial 5 waves being identifiable with certainty. The presence of a light-evoked, prominent vertex wave, dissimilar from that evoked by sound, was noteworthy in view of the virtual absence of an occipital response and severity of visual deficit.

Effect of Brain-Stem Lesions on Conditioned Responses of Cats

The possibility was explored that certain central brain-stem areas might be critical for the performance of conditioned reflexes. In 6 cats, large bilateral electrolytic lesions were placed in the medial diencephalon or mesencephalon and subsequently defined by histology. A tone served as conditional stimulus and foot-shock as unconditional stimulus. The EEG, respiration, and the EMG of the conditioned limb were recorded. Persistent low voltage, fast activity consistently reappeared in the EEG in 7 to 10 days and was seen even after destruction of over 100 mm3 of the mesencephalon, including the reticular formation. Conditioned reflexes usually appeared only when such faster EEG patterns were present. Conditioned reflexes and discrimination between tones could occur, however, during relatively high voltage, slow activity in the cortical areas sampled. Extensive lesions essentially transecting the ascending reticular system or destroying the posterior hypothalamus did not preclude conditioning. In contrast, one animal could not be retrained when lesions were in the mamillary area. It is concluded that the medial mesencephalic systems are not essential for this type of conditioning and that, if any essential system does exist, it is located in the region of the mamillary bodies, field H1 of Forel, center median, and the habenulopeduncular tract.

Electrocortical reactions associated with conditioned flexion reflexes

Abstract Cats with permanently implanted cortical electrodes were drugged with bulbocapnine and the EEG recorded continuously during the formation of flexion conditioned reflexes (CR). The drug has no readily detectable effect on rate of conditioning and usually produces such slow EEG patterns that electrocortical arousal reactions are well demarcated. Arousal reactions to a tonal conditional stimulus (CS) given alone soon cease to occur, but become more frequent as the CS is paired with an unavoidable shock to the leg 25–50 times a day over several days. In all cases the EEG reactions attain a high level of consistency before the first respiratory or flexion CRs appear, almost invariably accompany them, and can survive for some time after these somatic CRs are fully extinguished. There is a tendency, however, for the EEG arousal response to diminish with overtraining despite continuation of somatic CRs and shock reinforcement, and in certain instances somatic CRs can occur during relatively slow electrocortical activity. There was no evidence that the somatic CRs correlated with any localization of electrocortical reactions or alterations of cortical evoked potentials.

ELECTROENCEPHALOGRAPHIC PATTERNS OF THE TEMPORAL REGION IN NORMAL ADULTS.

A RECURRENT PROBLEM in the initial evaluation of the patient suspected of having intracranial disease is that of relevance of atypical electrical discharges arising over temporal regions to the disease process in question. Since the studies of Bussel and Silverman? and associates and Obrist and Henry,3 it has been recognized that unilateral or shifting temporal “foci” are much more common in nonneurologically impaired elderly subjects than had been previously supposed. This finding raises a question as to their frequency in normal young and middle-aged adults. The question is fundamental in respect to interpretation of the electroencephalogram, inasmuch as clinical experience indicates that electrographic abnormalities are detected more often over temporal than other cerebral region^.^-^ Not withstanding the major emphasis that has been placed upon electrographic findings for detection of functional disturbances of the temporal lobe in recent years, systematic normative data have not been generally available. This study was undertaken to provide information about incidence, form, and laterality of transient temporal discharges in adults below 60 years of age. The findings have been related to level of alertness of the subject, handedness, other characteristics of the electroencephalographic tracing, and potentially important medical findings.

Visually evoked responses in migraine

Abstract Visually evoked responses from the central and occipital areas were compared between 50 patients with migraine (during the headache-free period) and 46 control subjects. The findings suggest that migraine might be associated with altered cerebral responses to visual stimulation. Of three occipital surface negative components studied, the second (“intermediate” cluster) tended to appear slightly earlier in the migrainous individuals whereas the third (OIII) appeared later. Average amplitude of the second major surface positive wave (OIV) was lower. These differences were significant for the total experimental population and the female subgroup. Latency of the OII component (surface positive) was longer for females with migraine, a finding not present for the total population. No significant differences emerged between male experimental and control groups. Vertex responses were similar in migrainous and normal subjects. The routine EEG was abnormal in eleven of 50 (22%) patients. Average pupil size of the patients with migraine was significantly smaller than that of the controls.

OBSERVATIONS ON PHOTICALLY EVOKED OCCIPITAL AND VERTEX WAVES DURING SLEEP IN MAN

Information about the character of the visual evoked response in man during sleep and possible differences between waking and sleep is as yet limited. Vanzulli et a2. (1960) reported that response latencies were increased and “positive waves” augmented. CigLnek ( 1961 ) noted that the early triphasic complex was unchanged except for increased latency while a later wave (“V”) was increased in amplitude, broadened and delayed. He observed typical K-complexes during deep sleep. Guillard (1960) has reported that an anteriorly distributed response may persist in sleep when the posterior response has disappeared. He also reported longer response latency as depth of sleep increased. Brazier (1960) and Barlow (1960) have averaged occipital responses to flash in a subject both awake and asleep and have shown that periodic alpha range oscillations may disappear during sleep. The present communication describes morphological characteristics of cerebral responses evoked by single intense photic stimuli presented during sleep, compares these characteristics with those observed in waking and relates response morphology to electrographic and behavioral measures of level of consciousness. Attention is also given to topographical features of the responses, particularly in relation to distinctions that may be drawn between central and occipital events.

Fourteen and six c/sec positive bursts in comatose patients

Of ten patients with Reyes syndrome, there were five with stage II or III coma where EEGs revealed 14 c/sec positive bursts in a background of diffuse delta waves. Positive bursts disappeared upon EEG improvement in two survivors and when the EEG became nearly isoelectric in two other patients. Although 14 and 6 c/sec positive bursts are seen commonly during sleep in normal young persons, their occurence in association with diffuse delta waves in acutely ill, comatose patients has been rarely reported. It is not certain whether the present findings should be regarded as selective preservation of a type of sleep pattern or whether there are special factors that enhance positive bursts in stage II or III coma of Reyes syndrome.

The electroencephalogram in hepato-lenticular degeneration (Wilson's disease)

Abstract The literature on EEGs in hepato-lenticular degeneration has been reviewed; over half of 80 reported patients had abnormal tracings. Eight additional EEGs on seven patients are presented; two definitely abnormal, three borderline and three normal. Trends include continuous slowing of background frequency and sharp diphasic forms bicentrally and elsewhere. There is no specific EEG abnormality in this disease. Although there are many exeptions, in general the degree of EEG abnormality parallels the severity of clinical involvement. No individual clinical finding consistently relates to EEG abnormality, although there is a suggestion both from our cases and those previously reported that tremor and incoordination may show such a relationship. Some patients have EEG improvement during or after treatment; it is uncertain whether this change is cause-and-effect or coincidence. More studies of pre- and post-treatment EEGs would be of interest.