Reginald G. Bickford

Lambda responses in the human electroencephalogram.

SINCE LAMBDA WAVES were first reported by Evans1 in 1953, several studies, particularly those of GreenZ and of Gastaut and Bert,3 have added further information on the lambda mechanism. However, the present study contains a more detailed examination of the stimulus parameters of the lambda response than has been reported previously. In addition, the quantitation of lambda waves is undertaken mainly by direct measurement, although a brief reference to summation techniques will be made. In particular, the form, size, brightness, color, and movement of the visual stimulus necessary for the production of lambda waves has been examined. The relations between eye movement and the lambda wave as well as the similarity of the photic and the lambda responses were studied. Finally, the effects of certain psychologic variables, for example, fatigue, mental activity, and the hypnotic state, have been investigated.

Use of frequency discrimination in the automatic electroencephalographic control of anesthesia (servo-anesthesia)

Abstract 1. 1. Frequency analyses of electro-encephalograms of the cat indicate a progressive slowing combined with a fall in amplitude of all frequencies with deepening anesthesia with Pentothal sodium. 2. 2. Integration of a narrow band of frequencies centering on 8 cycles per second provides a method of automatic control of anesthesia with barbiturates which is almost entirely free from disturbance by artifacts. 3. 3. A similar method has been applied successfully to the automatic control of anesthesia with barbiturates in man.

Computer-controlled multidimensional display device for investigation and modeling of physiologic systems

Abstract A system is described in which the space- and time-sampled data can, by manipulation, be displayed as a variety of contoured structures according to the investigators preference. Additionally, the device can be used to display an appropriate model of the system under study, such as a dipole model of a potential field. The time dimension can be manipulated in a variety of ways, one of the most instructive being that of a movie-like display of the moment-to-moment spatial contours. The basic system consists of a digital computer which samples data from a specified electrode array, increases the number of data points 25-fold by statistical interpolation, and provides a variety of moving displays or graphic output options. The initial systems were digital but a hybrid system was eventually developed which provided maximal flexibility and efficiency for the medium-sized computer available.

Electroencephalographic diagnosis of brain tumors

Abstract The EEG is a screening method for organic focal lesions, particularly for cortical tumors, and to a lesser extent for subcortical and midline expanding lesions. With care in technic and interpretations, the neurologist and neurosurgeon are provided with a very useful and reliable method to supplement their clinical impressions.

Cardiovascular factors in limb tremor

UNDER NORMAL PHYSIOLOGIC CONDITIONS, when an attempt is made by means of a voluntary muscle effort to maintain a limb in a stationary position or to exert a constant force, a mechanical tremor can be detected in the limb. Various theories have been developed to account for the occurrence of this “physiologic” tremor, but none is entirely satisfactory.lr2 The current theories suggest that physiologic limb tremor may be due to one of the following mechanisms: [l] “driving” of the part at the relevant frequencies of oscillation by a neuromuscular input reflecting either a cyclic process in the central nervous system or an incomplete degree of desynchronization of muscle unit activity, [2] forcing of an underdamped resonant mechanical or reflex system by the asynchronous firing of muscle units over a wide range of frequencies, and [ 3 ] forcing of an underdamped resonant mechanical or reflex system by energy derived from the action of the heart. In view of the multiplicity of explanations of the origin of limb tremor, it seems possible that theories which propose a single underlying mechanism to account for this tremor may be incomplete. It is more likely that limb tremor is a composite phenomenon and that the magnitude of the contribution of any one mechanism will vaiy with the body site at which the tiernor is detected, with variation in the external mechanical support of the limb (so that tliffeient segments of the limb are involved individually or in combination in the oscillation of the part) and with changes in the level of contractile activity in the limb musculature. In the present investigation, the site at which the tremor was detected was kept constant (the index finger) during a sustained, constant,

CHANGES IN SUMMATED VISUAL POTENTIALS (LAMBDA WAVES) DURING MENTAL TASKS USING THE STROOP TEST

In normal Ss, a parietal-occipital located response (lambda wave) is evoked by scanning a printed block and word material (colored, and black and white) of the Stroop test. When this response is summated with a computer triggered by the eye movement, a highly reliable triphasic wave appears which can be subjected to accurate latency and amplitude measurements. The shortest latency of this response was observed when blocks vs words were presented, but there were no differences in latency in spite of increasing difficulty of material. This indicates that the structure of the material rather than mental activity affected the latency. Likewise, no changes were noted with colored vs black material. There was, however, a small increase in amplitude of the lambda wave response in the most difficult (word interference) task—a result that could be attributed equally to increase of muscle potentials and to the effect of mental activity.