Robert B. Malmo

Physiologic studies of reaction to stress in anxiety and early schizophrenia.

Physiologic Studies of Reaction to Stress in Anxiety and Early Schizophrenia ROBERT MALMO;CHARLES SHAGASS; Psychosomatic Medicine

Osmosensitive neurons in the rat's dorsal midbrain

In experiment 1, multiple unit recordings were taken simultaneously from lateral preoptic and dorsal midbrain areas during a series of intracarotid hypertonic and isotonic NaCl injections. Subjects were 15 hooded rats (11 males and 4 ovariectomized females) under urethane anesthesia. Results showed that the neuronal reactions to a series of hypertonic NaCl injections (0.30 M, 0.45 M, 0.60 M and 0.75 M) were at least as strong in the dorsal midbrain as in the lateral preoptic area. Strength of neuronal reaction correlated with osmolarity of the NaCl solution injected. Control isotonic NaCl injections were ineffective, and the (monitored) force of injection was found not to affect the results. In experiment 2 with 15 hooded rats (9 males and 6 ovariectomized females), and two male Wistar rats under urethane anesthesia, recording from dorsal midbrain units were made during intracarotid injections of hypertonic and isotonic NaCl solutions. In addition, other sensory stimulations, including tail pinches, were presented. Of the 52 units studied, 39 cells (75%) reacted to injections of hypertonic NaCl, but not the isotonic (control) solution (Normosol-R). Again, strength of neuronal reaction correlated with osmolarity of the NaCl solution injected, and force of injections was found not to influence results. Eleven cells reacted to hypertonic NaCl injections but not to tail pinch. This and other evidence indicated that certain dorsal midbrain cells were specifically osmosensitive, and not merely showing general arousal reactions to the injections. These results indicate that, for the rat, the osmosensitive zone extends into the midbrain. The functional significance of these findings is discussed.

Slowing of Heart Rate after Septal Self-Stimulation in Rats

In the report Slowing of heart rate after septal self-stimulation in rats, by R. B. Malmo [Science 133, 1128 (14 Apr. 1961)], there is a transposition of values for heart rate given in two successive sentences beginning with line 21, column 1, page 1129. The sentences should have read: Systematic quantitative analysis of the heart-rate data for this animal showed that mean heart rate for periods with self-stimulation was 389.4 beats per minute compared with 442.2 beats per minute for preceding periods without intracranial stimulation. Corresponding mean values for subjects 6 and 10 that also had the five full-training sessions were 442.8 and 451.2 for subject 6, and 400.8 and 428.4 for subject 10.

Rod and cone sensitivity in destriate monkeys

Photopic and scotopic spectral sensitivity of rhesus monkeys was determined before and after complete removal of the striate cortex. The monkeys were required to choose between a white and a series of monochromatic stimuli distributed throughout the visible spectrum. A modified method of limits was used to determine the psychophysical point of subjective equality at which the colored and white lights were perceived as being equally bright. The preoperative results indicated that the method of testing was appropriate to determine spectral sensitivity since the curves obtained compared favorably to the theoretical sensitivity curves. Postoperatively, the scotopic sensitivity curve was normal whereas the photopic curve was completely displaced towards the scotopic curve. The results as indicating that cone information is processed by the geniculo-striate visual system whereas the extra-striate structures receive their input mainly from the rod receptors of the retina.

Effects of striate cortex ablation on intensity discrimination and spectral intensity distribution in the rhesus monkey

Abstract In order to study residual vision in rhesus monkeys following removal of the occipital lobes, (a) difference limens at photopic and scotopic levels were obtained pre- and post-operatively, and (b) the relative visibility of different regions of the spectrum was studied with normals and operates. The visibility curve obtained under photopic conditions postoperatively was shifted very markedly in the direction of the scotopic visibility curve; and scotopic brightness discrimination appearred less impaired by operation than photopic discrimination. These findings and the histological data are considered in relation to current issues concerning neural bases of vision.

On electromyographic (EMG) gradients and movement-related brain activity: significance for motor control, cognitive functions, and certain psychopathologies.

Electromyographic (EMG) voltage that rises continuously during motor performance or mental activity and falls precipitately at the end is known as an EMG gradient. Our review is based on 55 studies of EMG gradients, which were published during the period 1937-1994. The extremely wide diversity of situations yielding EMG gradients suggests the possibility that these gradients may be universal accompaniments of organized goal-directed behavioral sequences, overt and covert. Motor tasks and cognitive tasks (without any requirements for motor output) were found to have this in common: they both produced EMG gradients. EMG gradients were not observed during simple, repetitive exercises. On the efferent side, we propose a dual model for the production of EMG gradients, which is based on empirical findings. This model is discussed in relation to current views on central and peripheral neural control of muscle contractions, and on the electrical properties of extrafusal and intrafusal muscle fibers, with particular reference to surface electromyography. The complex relations between EMG gradient steepness and mental effort seemed well represented by the dual model, which was also useful in the interpretation of certain EMG gradients that were found in patients with anxiety disorders, tension-type headaches, and auditory hallucinations, respectively. On the afferent side, drawing on data from human and animal studies, we consider the evidence for movement-related brain activity generated by proprioceptive input, in relation to different types of feedback to the central nervous system during tasks that produce EMG gradients. On electromyographic (EMG) gradients and movement-related brain activity: significance for motor control, cognitive functions, and certain psychopathologies.

Electrophysiological concomitants of simple operant conditioning in the rat

Abstract While rats learned to press a lever for food, both heart rate (HR) and subcortical EEGs developed significant bitonicity in the period ranging from a few seconds before to a few seconds after responses. The HR curve was an inverted-V, with the peak value located at the moment of response and falling off regularly on either side. EEGs recorded from septum, hippocampus, midbrain tegmentum, and central gray substance were electronically analyzed in a frequency band of 16–28 Hz. Bitonic EEGs, which were obtained from all placements except the motor cortex, were phased oppositely to HR (i.e. U-shaped), with the trough coinciding with the response. HR bitonicity develops earlier than EEG bitonicity, but both trends disappear very rapidly in extinction. Evidence is presented indicating that response-oriented, electrophysiological bitonicity is a neural correlate of reinforcement.

Experiments on the neuropsychology of thirst

We report the results of a series of experiments whose main objectives are: (a) the identification of neural receptors for thirst; and (b) other neural structures of critical importance for thirst and drinking behavior. We have used results from hypertonic challenges during acute unit and multiple-unit recording experiments to identify responsive brain areas for behavioral study in chronic experiments. Results include the following. Single cells in the lateral preoptic area (LPOA) responded to injections of hypertonic saline into the carotid artery in a dose-related manner. Multiple unit activity (MUA) reactions were invariably facilitatory to challenge, and were much greater in the LPOA than in the medial preoptic area (MPOA). In unit and MUA recording we found extremely osmosensitive sites in the dorsal midbrain. Comparing the effects of NaCl vs sucrose as challenges via the intracarotid artery we found that LPOA MUA responses to sucrose were at least as strong and latencies as short as those to NaCl. These results support osmoreceptor theory, as revised by Epstein and his co-workers, and they are opposed to Anderssons sodium receptor theory. Hypertonic NaCl and sucrose solutions (but not artificial CSF controls) injected into the lateral ventricle were effective in producing strong MUA reactions, which typically were inhibition followed by facilitation. These and other findings support the following conclusions. (a) The LPOA appears to be a vital part of the neural mechanism for thirst and it is a probable site of osmoreceptors. (b) In addition, the LPOA seems to be a receiving area connected with putative periventricular neural receptors. (c) Intraventricular (i.v.t.) angiotensin II seems to be a much stronger dipsogen than hypertonic NaCl i.v.t., which in higher concentrations elicited stereotyped running.

Individual consistency and modifiability of lapping rates in rats: A new look at the variance-invariance question

Lapping rates were recorded from water-deprived rats over 3-week periods when they were young adults and again, 9.4 months later, when they were middle-aged. Test-retest correlation coefficients of 0.95, that were obtained for lapping rates recorded as long as a week apart, reflect extremely consistent frequency control, which is in line with the proposal by Wiesenfeld et al. (1977) that licking/lapping is under control of a hypoglossal oscillator. These high test-retest correlations were obtained both in young adulthood and again, later in middle-aged rats. However, correlations across the 9.4 months were close to zero, although mean water lapping rate did not change. Our data indicate that the effects of aging on lap rate were of two kinds. (1) Producing randomized shifts in the lapping rate of individual rats over long periods, with conservation of the stable mean rate, and (2) accentuating the tendency for reduction in the lapping rate for the last 50 laps compared with that of the first 50. It also appeared that the relevance of the fluid being lapped, in relation to water deprivation, was another important variable in determining the lapping rate. These and other data are considered in relation to the variance-invariance issue.

Cardiovascular and respiratory responses to electrical stimulation of the midbrain in the rat

In descending through the midbrains of rats with stimulation electrodes, we have observed some remarkable reversals of pressor and depressor autonomic effects as the electrode was moved from one locus to another. Autonomic effects of stimulating in the midbrain areas that we studied are of special interest because stimulations in some of these midbrain loci have pain-relieving effects (Hosobuchi et al., 1977, 1979; Mayer et al., 1971; Soper, 1976). Our observations of cardiac arrest are of particular concern because of the use that is being made of midbrain electrical stimulation to relieve pain in human patients.