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PubMed1983

Testing a theory of brain function by computer methods. II. Timing short-range mental scanning.

In keeping with a plan for overall testing of the timing and sequencing of brain processes, testing techniques are introduced for timing short-range mental scanning without eye movement. The tests, using a personal computer, reveal the tendency to scan from left to right, even when there is insufficient time for eye movement, in persons whose first language is one which is read from left to right. The tests depend on the use of blocking stimuli which operate on central processes rather than peripheral processes, and suggest that it is possible to measure the timing and sequencing of central brain processing thereby.

Adult↗

PubMed2002

High-tech brains: a history of technology-based analogies and models of nerve and brain function.

This article reviews some of the technological devices and ideas which have been used over the years to answer the question, how does the brain work? It describes some of the early technology-based analogies and models of nerve fibers, and then discusses other analogies and models of the brain based on mechanical and electrical technologies. There are also short sections on cybernetics, telephone exchanges, and computers. Although all of these ideas are flawed to some extent, this article offers a brief argument on the usefulness of analogy and abstraction in brain science.

Brain↗

PubMed1992

The 5 alpha-reductase in the brain: molecular aspects and relation to brain function.

All the classes of hormonal steroids physiologically produced in the body (androgens, estrogens, progestagens, and corticosteroids) are able to exert important effects on the brain, but the mechanisms of their actions are not always well understood. Steroids may interact with intracellular receptors to activate the genome, but some of their effects are probably extragenomic and involve interactions with cellular membranes. Moreover, not all the steroids act always in their native molecular form; a large group of them must actually be transformed into "active" metabolites. This may occur at the level of their respective target structures. For example, androgens are metabolized in the brain into estrogens and into 5 alpha-reduced androgens, like 5 alpha-androstan-17 beta-ol-3-one (dihydrotestosterone; DHT) and 5 alpha-androstan-3 alpha, 17 beta-diol (3 alpha-diol). Progesterone, and possibly corticosteroids, may also be transformed into their corresponding 5 alpha-reduced metabolites. Also the cellular target (neurons and/or glial cells) of the hormonal steroids in the brain is not always clear. This review analyzes in detail one of the two major enzymatic systems that transform steroids in the brain, namely the 5 alpha-reductase-3 alpha-(3 beta)-hydroxysteroid dehydrogenase pathway. An active 5 alpha-reductase-3 alpha-hydroxysteroid dehydrogenase system is widely distributed in practically all CNS structures in all phases of development. In the brain, this enzymatic system is not regulated by castration or sex steroid administration; furthermore, neural inputs seem to be ineffective at the hypothalamic level. A recent interesting finding is the presence of high concentrations of the 5 alpha-reductase in the white matter. This probably is due to the fact that the white matter is particularly rich in myelin membranes, with which the enzymatic activity appears to be associated. An active 5 alpha-reductase activity has also been shown to be present in peripheral myelinated nerves. The localization in myelin membranes may suggest a possible involvement of 5 alpha-reduced metabolites of the different steroids in the process of myelination. The presence of the 5 alpha-reductase was analyzed in neurons, astrocytes, and oligodendrocytes isolated from the brains of male rats, as well as in neurons and glial cells grown in culture. Neurons appear to be more active than glial cells in converting testosterone into DHT. Only neurons possess aromatase activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2005

Emotional and autonomic consequences of spinal cord injury explored using functional brain imaging.

In health, emotions are integrated with autonomic bodily responses. Emotional stimuli elicit changes in somatic (including autonomic) bodily states, which feedback to influence the expression of emotional feelings. In patients with spinal cord injury (SCI), this integration of emotion and bodily arousal is partially disrupted, impairing both efferent generation of sympathetic responses and afferent sensory feedback of visceral state via the spinal cord. A number of theoretical accounts of emotion predict emotional deficits in SCI patients, particularly at the level of emotional feelings, yet evidence for such a deficit is equivocal. We used functional MRI (fMRI) and a basic emotional learning paradigm to investigate the expression of emotion-related brain activity consequent upon SCI. We scanned seven SCI patients and seven healthy controls during an aversive fear conditioning task. Subjects viewed randomized presentations of four angry faces. One of the faces (CS + arm) was associated with delivery of electrical shock to the upper arm on 50% of trials. This shock was painful to all subjects. A face of the same gender acted as a 'safe' control stimulus (CS - arm). In both control subjects and SCI patients, painful cutaneous stimulation of the arm evoked enhanced activity within components of a central pain matrix, including dorsal anterior cingulate, right insula and medial temporal lobe. However, SCI patients differed from controls in conditioning-related brain activity. SCI patients showed a relative enhancement of activity within dorsal anterior cingulate, periaqueductal grey matter (PAG) and superior temporal gyrus. Conversely, SCI patients showed relative attenuation of activity in subgenual cingulate, ventromedial prefrontal and posterior cingulate cortices to threat of painful arm stimulation (CS + arm > CS - arm). Our findings provide evidence for differences in emotion-related brain activity in SCI patients. We suggest that the observed functional abnormalities including enhanced anterior cingulate and PAG reflect central sensitization of the pain matrix, while decreased subgenual cingulate activity may represent a substrate underlying affective vulnerability in SCI patients consequent upon perturbation of autonomic control and afferent visceral representation. Together these observations may account for motivational and affective sequelae of SCI in some individuals.

Anger↗

PubMed1971