Loss of cortical control over the descending pain modulatory system determines the development of the neuropathic pain state in rats

The loss of descending inhibitory control is thought critical to the development of chronic pain but what causes this loss in function is not well understood. We have investigated the dynamic contribution of prelimbic cortical neuronal projections to the periaqueductal grey (PrL-P) to the development of neuropathic pain in rats using combined opto- and chemogenetic approaches. We found PrL-P neurons to exert a tonic inhibitory control on thermal withdrawal thresholds in uninjured animals. Following nerve injury, ongoing activity in PrL-P neurons masked latent hypersensitivity and improved affective state. However, this function is lost as the development of sensory hypersensitivity emerges. Despite this loss of tonic control, opto-activation of PrL-P neurons at late post-injury timepoints could restore the anti-allodynic effects by inhibition of spinal nociceptive processing. We suggest that the loss of cortical drive to the descending pain modulatory system underpins the expression of neuropathic sensitisation after nerve injury.

Line bisecting as a predictor of personal optimism and desirability of risky behaviors

Our goal was to test whether current hemisphere predominance is a predictor of scores on standardized measures of personal optimism and preference for risk. In two between-subject experiments, current hemisphere predominance was measured by the direction and extent of line bisecting errors. Pearson correlations and median splits of the line bisecting errors showed significantly greater personal optimism and preference for risk with left hemisphere predominance. These results support previous research in which manipulation of hemisphere predominance produced similar effects on personal optimism in normal individuals and on risk taking in lesioned and normal samples. We conclude that the association of optimism and risk with left hemisphere predominance can be observed in resting as well as in manipulated situations.

Processing persuasive arguments: recall and recognition as a function of agreement and manipulated activation asymmetry

Previous research has demonstrated greater attention toward disagree arguments and a greater persuasibility during relative right than during relative left hemisphere activation. This experiment was performed to conceptually replicate and extend these findings to memory stages in the processing of persuasive arguments. The experiment used induction of lateral orientation of attention as the means to selectively activate regions of the brain in normal right-handed subjects. The results showed the expected significant interaction for correct recall as a function of agreement with the argument and hemisphere activated. There was greater recall of agree arguments during left hemisphere activation and greater recall of disagree arguments during right hemisphere activation, as predicted. The effect for recognition memory was in the same direction, but was statistically nonsignificant. These findings support previous research on cerebral asymmetries in the processing of persuasive arguments. This phenomenon is discussed as a possible outcome of asymmetries of affect.

Cognitive spatial-motor processes. 5. Specification of the direction of visually guided isometric forces in two-dimensional space: time course of information transmitted and effect of constant force bias

The effects of an external constant force bias on the information transmitted (Ti) by the direction of isometric force exerted in 2-dimensional (2-D) space by human subjects were studied using an isometric manipulandum and random dot stereograms generated in a color display (Massey et al. 1988, Massey et al. 1990). Subjects exerted force on the manipulandum such that a visual force-feedback cursor would move in the direction of a visually defined stimulus in the stereo display. The time course of force development and the gain of directional information during increasing force intensity were also studied. We found the following. (a) When no bias force was applied, the force exerted by the subject increased from near zero to greater than 200 gram-force at the end of a trial and was close to the visually defined direction. When a constant bias force of 110 gram-force was applied in various directions in blocks of trials, the force exerted by the subject increased in time, as above; however, its direction also changed in time so that the instantaneous vector sum of the bias force and the force exerted by the subject pointed close to the visually defined direction. The Ti and the reaction time (RT) did not differ significantly in the two experimental conditions. These results suggest that the directional control of isometric forces is very efficient, especially in relation to visuomotor coordination. (b) The Ti was calculated at various levels of force intensity, as the latter increased from approximately 50 gram-force to 200 gram-force.(ABSTRACT TRUNCATED AT 250 WORDS)

Cognitive spatial-motor processes. 4. Specification of the direction of visually guided isometric forces in two-dimensional space: information transmitted and effects of visual force-feedback

The information transmitted (Ti) by the direction of two-dimensional (2-D) isometric forces at different stereoscopic depths was studied in 50 naive human subjects using an isometric manipulandum and random dot stereograms generated in a color display (Massey et al. 1988). Subjects viewed the display through appropriate color filters and perceived the image of a disk rotated about a horizontal axis on the frontal plane; the top of the disk was rotated around that axis by 15, 45, 60 and 80 degrees away from the subject. Each of these disks involved a different amount of stereoscopic depth perception which was lowest for the 15 degrees and highest for the 80 degrees tilt. Subjects were instructed to exert force in the direction of a visual target presented on the disk in a reaction time task. The instantaneous force exerted by the subjects on the manipulandum was shown on the disk in the form of a feedback cursor. Information transmitted, reaction time (RT) and systematic directional deviations were calculated. We found the following. (a) Ti increased with input information but at a lower rate; at the highest level of input information studied (5.91 bits), Ti was 4.1 bits at the 15 degrees tilt. This high value of Ti suggests that directional information for isometric force is processed very efficiently. However, this Ti was consistently lower than that transmitted by the direction of movement (Georgopoulos and Massay, 1988). (b) Ti did not differ significantly among the 15-60 degrees tilt but was 0.19 bits less for the 80 degrees tilt. RT did not differ among the 15-80 degrees tilts.(ABSTRACT TRUNCATED AT 250 WORDS)

Toward a model to explain infant preferences by cerebral emotional asymmetry and hemisphere priming

This paper argues that the rightward preference observed in most infants can be described as the consequence of two characteristics of the human brain: (1) hemispheric asymmetry of processes underlying emotional experience and (2) priming of cerebral function. Ample research evidence supports each of these propositions, and they have gained increasing, though not universal, acceptance. In combination, they provide a sufficient explanation for several preferences which may have human survival value. They also produce several side-effects in human behavior which can be observed, but which appear to have no survival function.

Self-serving biases in causal attributions as a function of altered activation asymmetry

The method of induced lateral orientation of attention was selectively used to alter the balance of activation of the brain toward one cerebral hemisphere or the other. The goal was to extend earlier research which showed greater personal optimism for future events during left hemisphere activation to the related phenomenon of causal attributions. As predicted, there was significantly greater self-serving bias (attribution of internal, stable, and global causes for positive events and external, unstable, and specific causes for negative events) during left hemisphere than during right hemisphere relative activation. This was true for achievement but not for affiliation events. These effects were explained in terms of the increased positive affect which correlates with greater left hemisphere activation. Selective activation of the left hemisphere as a means temporarily to alter attributional style was discussed as a possible tool in the treatment of learned helplessness and depression.

A role for hemispheric asymmetry in human behavioral variability

A model is presented in which functional lateral specialization and selective hemisphere priming combine to provide a mechanism for behavioral variability. The model is tested and supported by two experiments in which lateral attentional priming produces significant reductions in between-subject and within-subject variability. These findings help us to understand the source of behavioral variability, broaden our knowledge of the gross structures and functions of the brain, provide information about the manipulation of perceived control, and offer a technique for increasing statistical power in a wide variety of research settings.

Optical biosensors for immunoassays: the fluorescence capillary-fill device

This paper reports, for the first time, details of a novel type of optical biosensor for immunoassays, the fluorescence capillary-fill device (FCFD). This is based on a straightforward adaptation of the technology used to mass manufacture liquid-crystal display (LCD) cells to give cheap disposable immunosensors. These merely require contact by the sample to give a result in about a minute, and use certain principles of optical fibres and waveguides to avoid the need for operator attention, for physical separation methods or for washing steps. After a very brief introductory review and classification of optical biosensors, the main features of the FCFD and its associated instrumentation are described. The optical characteristics of the FCFD are then described, followed by accounts of the immunoassay method, the measurement system used in the experiments, the fabrication of FCFD sensors and a detailed description of the design of a competitive immunoassay for human immunoglobulin G (hIgG). The experimental details and the results of a first attempt at such an assay are then presented and discussed. It is concluded that the demonstration of this assay is a significant achievement, because the format of the FCFD, its manufacturing process and its instrumentation are completely novel. Certain problem areas have been identified and quantified; intended further work on these is outlined.

Lateral asymmetry of impression formation

On the premise that the more complex functions are those which are more asymmetrically represented in the human brain, it was suggested that it would be possible to measure differences in the impression formed of another person as a function of the relative activation of the cerebral hemispheres. Selective activation was manipulated by the induction of lateral orientation of attention. A pilot study produced the predicted significant results: A more positive impression was formed by right handers whose right hemisphere was activated by leftward attentional orientation. This effect was replicated in the main experiment. These findings support previous research which showed that attention to the self is increased with relative left hemisphere activation while attention to external stimuli is enhanced during a relative right hemisphere pattern of activation.

Left cerebral hemisphere contributions to tachycardia: evidence and recommendations

Six topics were discussed in which research has shown a stimulus or activity to be independently related to increases in human heart rate and to left cerebral hemisphere functioning: lateralized touching, reasoning, pleasantness, talking, lateralized feedback, and resistance to persuasion. On the basis of this converging evidence, strategies were suggested for altering heart rate by use of the method of induced lateral orientation of attention as a means of selective hemisphere activation.

Induced lateral orientation and persuasibility

It was hypothesized from three different lines of evidence that relative activation of the left cerebral hemisphere of right-handers would increase resistance to a persuasive message as compared to relative activation of the right hemisphere. An experiment was performed using 22 subjects who heard the counterattitudinal message in only one ear and filled in response measures while their body was turned toward that same side. Subjects who listened and turned toward the left agreed more with the views of the message (p less than .05) and produced more thought favorable to the message (p less than .05) than those induced to orient rightward. It was concluded that these results may be due to asymmetries in selective attention, counterarguing, consistency, self-awareness, and perseveration between the cerebral hemispheres of the normal human brain.

Familiarity-and-liking relationship under conditions of induced lateral orientation

Right-handed subjects who oriented their bodies and their attention toward their right produced a significant relationship between their rated familiarity with and liking for several well-known individuals. Those induced to orient toward their left showed no such effect. It is argued that such orientation produces relatively greater activation of the contralateral hemisphere, and experiments and reviews are cited which show that the left hemisphere has been suggested as the site for both processing of familiar stimuli and positive affect. Even if familiarity does activate liking by some means by virtue of being predominantly processed in the same hemisphere, it is not known how this occurs nor how it is altered by lateralized attention.