Visual perception: mind and brain see eye to eye. (1/271)

Recent functional imaging studies have identified neural activity that is closely associated with the perception of illusory motion. The mapping of the mind onto the bin appears to be one-to-one: activity in visual 'motion area' MT is highly correlated with perceptual experience.  (+info)

Neurosciences - A neurosurgeon's perspective. (2/271)

The advancements in the field of science in the past fifty years have highlighted the need to integrate all fields of human endeavours and have emphasised interdependency of various disciplines. The separation of humanities, therefore, from neurosciences is a preposterous practical joke on all thinking men. With the human genome project on the anvil, biotechnology is making significant headway holding out promise for organ regeneration. Macro evolution is over, but micro-evolution continues in the brain. Neural Darwinism thus, continues to evolve as long as individual remains conscious and has memory. In the milieu of widely varying internal physiological mechanisms and external stimuli, an alternative theory to preprogrammed directionalism is proposed by three mechanisms namely developmental variation and selection, experiential selections and reentrant signalling. Reentrant signalling reorients and correlates the external inputs leading to psychic development preceding the development of consciousness. The cholinergic and aminergic neuro-modelling systems are well suited to serve as value systems. The main achievement of consciousness is to bring together the many categorizations involved in perceptions into a SCENE. Another part of evolution involved capacity of reentrant signalling to be guided by a value system where it is provided with a lot of choices. With 10(13) neurons and 10(16) connections, freedom of choice may manifest into a 'Buddha' or a 'Hitler'. As part of the evolutionary process, it was interesting how capacity to categorize the need to worship by referring to environment outside evolved into a search within our minds. As the next stage of evolution, neuroscience may, thus, serve as the next gateway to understanding the mind and soul.  (+info)

Neuroendocrine and psychophysiologic responses in PTSD: a symptom provocation study. (3/271)

Biological research on post-traumatic stress disorder (PTSD) has focused on autonomic, sympatho-adrenal, and hypothalamo-pituitary-adrenal (HPA) axis systems. Interactions among these response modalities have not been well studied and may be illuminating. We examined subjective, autonomic, adrenergic, and HPA axis responses in a trauma-cue paradigm and explored the hypothesis that the ability of linked stress-response systems to mount integrated responses to environmental threat would produce strong correlations across systems. Seventeen veterans with PTSD, 11 veteran controls without PTSD, and 14 nonveteran controls were exposed to white noise and combat sounds on separate days. Subjective distress, heart rate, skin conductance, plasma catecholamines, ACTH, and cortisol, at baseline and in response to the auditory stimuli, were analyzed for group differences and for patterns of interrelationships. PTSD patients exhibited higher skin conductance, heart rate, plasma cortisol, and catecholamines at baseline, and exaggerated responses to combat sounds in skin conductance, heart rate, plasma epinephrine, and norepinephrine, but not ACTH. The control groups did not differ on any measure. In canonical correlation analyses, no significant correlations were found between response systems. Thus, PTSD patients showed heightened responsivity to trauma-related cues in some, but not all, response modalities. The data did not support the integrated, multisystem stress response in PTSD that had been hypothesized. Individual response differences or differing pathophysiological processes may determine which neurobiological system is affected in any given patient.  (+info)

Psychosocial aspects of the functional gastrointestinal disorders. (4/271)

The functional gastrointestinal disorders (FGID) are the most frequent conditions seen in gastroenterology practice and comprise a major portion of primary care. Psychosocial factors are important in these disorders with regard to: (1) their effects on gut physiology; (2) their modulation of the symptom experience; (3) their influence on illness behavior; (4) their impact on outcome; and (5) the choice of the therapeutic approach. This paper provides a review and consensus of the existing literature by gastroenterologists, psychiatrists, psychologists, physiologists, and health services investigators. Evidence is provided to support the biopsychosocial model as a basis for understanding and treating these disorders, and epidemiological and clinical information on the relations of psychosocial factors to gut physiology, symptom presentation, health behavior, and outcome is offered. Features of motility, personality, abuse history, health concerns, and treatment-seeking differ between patients with FGID and healthy controls, but they are not specific to FGID. They occur in other patients with chronic medical conditions and/or psychiatric disorders. Review of treatment trials indicates clear support for psychotherapeutic treatments, especially in the long term, as well as some evidence for the benefit of antidepressants in FGID, even in the absence of improvements in mood.  (+info)

Individual differences in physiological responses and type A behavior pattern. (5/271)

The relationships between individual differences in psychophysiological responses and tendency of Type A behavior pattern (TABP) were investigated during mental arithmetic (MA) at a steady rhythm, challenging calculation (Uchida-Kraepelin serial addition test: UK test), music listening, and exposure to an 80 dB SPL of white noise. Each mental task was sustained for 5 minutes. Sixteen healthy Japanese adults, (10 males and 6 females) with an age from 18 to 36 years old volunteered for this study. The KG's Daily Life Questionnaire (KG Questionnaire) was used to investigate the tendency toward TABP, which included three sub-factors: aggression-hostility, hard-driving and time urgency, and speed-power items. Recorded physiological variables were respiratory rate (RR), skin resistance response (SRR), eyeblinks, and heart rate (HR) calculated using frequency analysis to render high frequency power (HF) and the ratio of low/high frequencies (L/H ratio). During the MA and UK tests, significant increases in HR, L/H ratio, RR occurred, while significant decreases in HF were observed. Eyeblinks significantly increased during the MA test and significantly decreased during the UK test. During music and white noise, no significant changes occurred except for SRR, which decreased significantly. The coefficient of variances in each response was over 20% for almost all variables, indicating that individual differences in the magnitude of each response were large, even if the direction (increase or decrease) of the change was the same in almost all subjects. The highest correlation coefficients (r) between the mean values of relative magnitude for each variable and TABP scores during the MA and UK tests were obtained for the L/H ratio (MA: r = 0.591, UK test: r = 0.577) and the RR (MA: r = -0.576, UK test: r = -0.511). These values were statistically significant (p < 0.05). Similar results were obtained for TABP sub-factors. Though other investigations have reported relationships between HF and TABP, we found no significant relationship. It was suggested that sympathetic nerve activity became greater for TABP individuals than for Type B individuals under stress conditions.  (+info)

The challenge of non-invasive cognitive physiology of the human brain: how to negotiate the irrelevant background noise without spoiling the recorded data through electronic averaging. (6/271)

Brain mechanisms involved in selective attention in humans can be studied by measures of regional blood flow and metabolism (by positron emission tomography) which help identify the various locations with enhanced activities over a period of time of seconds. The physiological measures provided by scalp-recorded brain electrical potentials have a better resolution (milliseconds) and can reveal the actual sequences of distinct neural events and their precise timing. We studied selective attention to sensory inputs from fingers because the brain somatic representations are deployed over the brain convexity under the scalp thereby making it possible to assess distinct stages of cortical processing and representation through their characteristic scalp topographies. In the electrical response to a finger input attended by the subject, the well-known P300 manifests a widespread inhibitory mechanism which is released after a target stimulus has been identified. P300 is preceded by distinct cognitive electrogeneses such as P40, P100 and N140 which can be differentiated from the control (obligatory) profile by superimposition or electronic subtraction. The first cortical response N20 is stable across conditions, suggesting that the first afferent thalamocortical volley is not affected by selective attention. At the next stage of modality-specific cortex in which the sensory features are processed and represented, responses were enhanced (cognitive P40) only a very few milliseconds after arrival of the afferent volley at the cortex, thus documenting a remarkable precocity of attention gain control in the somatic modality. The physiology of selective attention also provides useful cues in relation to non-target inputs which the subject must differentiate in order to perform the task. When having to tell fingers apart, the brain strategy for non-target fingers is not to inhibit or filter them out, but rather to submit their input to several processing operations that are actually enhanced when the discrimination from targets becomes more difficult. While resolving a number of such issues, averaged data cannot disclose the flexibility of brain mechanisms nor the detailed features of cognitive electrogeneses because response variations along time have been ironed out by the bulk treatment. We attempted to address the remarkable versatility of humans in dealing with their sensory environment under ecological conditions by studying single non-averaged responses. We identified distinct cognitive P40, P100, N140 and P300 electrogeneses in spite of the noise by numerically assessing their characteristic scalp topography signatures. Single-trial data suggest reconsiderations of current psychophysiological issues. The study of non-averaged responses can clarify issues raised by averaging studies as illustrated by our recent study of cognitive brain potentials for finger stimuli which remain outside the subject's awareness. This has to do with the physiological basis of the 'cognitive unconscious', that is, current mental processes lying on the fringe or outside of phenomenal awareness and voluntary control, but which can influence ongoing behaviour. Averaged data suggest that, in selective auditory attention, the subject may not notice mild concomitant finger inputs. The study of non-averaged responses documents the optional and independent occurrence of the cognitive P40, P100 and N140 (but not P300) electrogeneses while the finger inputs remain outside phenomenal awareness. These results suggest that the subject unconsciously assigns limited cognitive resources to distinct somatic cortical areas thereby submitting finger inputs to an intermittent curtailed surveillance which can remain on the fringe or outside consciousness. The study of cognitive electrogeneses in single non-averaged responses is making possible a neurophysiology of cognition in real time.  (+info)

Motion contrast: a new metric for direction discrimination. (7/271)

The Adelson-Bergen energy model (Adelson, E. H., & Bergen, J. R. (1985). Spatiotemporal energy models for the perception of motion. Journal of the Optical Society of America A, 2, 284-299) is a standard framework for understanding first-order motion processing. The opponent energy for a given input is calculated by subtracting one directional energy measure (EL) from its opposite (ER), and its sign indicates the direction of motion of the input. Our observers viewed a dynamic sequence of gratings (1 c/deg) equivalent to the sum of two gratings moving in opposite directions with different contrasts. The ratio of contrasts was varied across trials. We found that opponent energy was a very poor predictor of direction discrimination performance. Heeger (1992). Normalization of cell responses in cat striate cortex. Visual Neuroscience, 9, 181-197) has suggested that divisive inhibition amongst striate cells requires a contrast gain control in the energy model. A new metric can be formulated in the spirit of Heeger's model by normalising the opponent energy (EL - ER) with flicker energy, the sum of the directional motion energies (EL + ER). This new measure, motion contrast (EL - ER)/(EL + ER), was found to be a good predictor of direction discrimination performance over a wide range of contrast levels, but opponent energy was not. Discrimination thresholds expressed as motion contrast were around 0.5 +/- 0.1 for the sampled drifting gratings used in our experiments. We show that the dependence on motion contrast, and the threshold of about 0.5, can be predicted by a modified opponent energy model based on current knowledge of the response functions and response variance of cortical cells.  (+info)

Marijuana smoking and reduced pressure in human eyes: drug action or epiphenomenon? (8/271)

Normal pressure within the human eye was reduced after smoking a socially relevant dose of marijuana (12 mg. delta9-9-tetrahydrocannabinol), but only for light to moderate users who experienced a substantial "high" and a state of peaceful relaxation from the experimental dose. Analysis suggests an indirect effect of the drug associated with relaxation-a psychophysiologic state that can be produced by drug and nondrug means.  (+info)

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