PubMed · 6579656
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R Saladin. 1983. [Are we correctly programmed?].. https://pubmed.ncbi.nlm.nih.gov/6579656/
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1. The threshold for obtaining EMG responses after transcranial magnetic stimulation of the brain is reduced by voluntary contraction of the target muscle. The present experiments tested whether some of this effect is due to increased cortical, as opposed to spinal, excitability during the contraction. 2. Magnetic stimulation was delivered with a figure-of-eight coil oriented with the junction region along the interaural line and also (in 4 of 7 subjects) with a circular coil centred at the vertex. The intensity of the conditioning stimulus was subthreshold for evoking a motor response in the relaxed wrist flexor muscles of the forearm. The presence of a small descending corticospinal volley in both the relaxed and active conditions was detected by measuring the facilitation of test H reflexes elicited in the flexor muscles of the forearm. 3. In all subjects, magnetic stimulation with either coil facilitated the H reflex at conditioning-test intervals of -1 to -3 ms (median nerve stimulus before magnetic). This was followed by a long-lasting facilitation. In three of the seven subjects stimulation with the figure-of-eight coil elicited an additional, earlier peak of facilitation at a conditioning-test interval of -3 to -5 ms. 4. In all subjects, the threshold for obtaining facilitation of the H reflex using a conditioning-test interval of -1 to -3 ms was reduced, and the amount of facilitation was larger, if subjects performed a weak tonic voluntary contraction. In contrast, with a conditioning-test interval of -3 to -5 ms voluntary contraction had no effect on the threshold. 5. It is suggested that H reflex facilitation at the conditioning-test interval of -1 to -3 ms was produced by indirect activation of corticospinal neurones by the magnetic stimulus, whereas at -3 to -5 ms, the facilitation was produced by direct activation of corticospinal axons. It is concluded that tonic voluntary contraction of a target muscle decreases the threshold for indirect activation of corticospinal neurones but not for direct stimulation of their axons.
The purpose of this article is to review the research on the effectiveness of work hardening and work conditioning programs. Twelve studies of work hardening and work conditioning programs in the United States and abroad were reviewed. One study produced convincing evidence in a randomized study that a work conditioning program was useful in producing a higher percentage of return to work and an earlier return to work in a group of patients off work for at least 2 months. Another study demonstrated that a work hardening program increased the rate of return to work by 52% in patients off work for greater than 4 months. Most of the other studies reviewed suggested positive results, but more carefully documented, randomized, and controlled studies are needed to support the efficacy of these programs and to determine the optimum and most cost-effective work hardening and work conditioning interventions.
The acquisition and extinction of the conditioned suppression or enhancement of one or another parameter of antigen-specific and nonspecific defense system responses have been documented in different species under a variety of experimental conditions. Similarly, stressful stimulation influences antigen-specific as well as nonspecific reactions. Moreover, both conditioning and stressful stimulation exert biologically meaningful effects in the sense that they can alter the development and/or progression of what are presumed to be immunologically mediated pathophysiologic processes. These are highly reproducible phenomena that illustrate a functional relationship between the brain and the immune system. However, the extent to which one can generalize from one stressor to another or from one parameter of immunologic reactivity to another is limited. Few generalizations are possible because the direction and/or magnitude of the effects of conditioning and "stress" in modulating immune responses clearly depend on the quality and quantity of the behavioral interventions, the quality and quantity of antigenic stimulation, the temporal relationship between behavioral and antigenic stimulation, the nature of the immune response and the immune compartment in which it is measured, the time of sampling, a variety of host factors (e.g. species, strain, age, sex), and interactions among these several variables. It seems reasonable to assume that the immunologic effects of behaviorally induced neural and endocrine responses depend on (interact with) the concurrent immunologic events upon which they are superimposed. Conversely, the efficacy of immunologic defense mechanisms seems to depend on the neuroendocrine environment on which they are superimposed. We seek to determine when and what immunologic (or neuroendocrine) responses could be affected by what neuroendocrine (or immunologic) circumstances. We therefore need studies that provide a parametric analysis of the stimulus conditions, the neuroendocrine and/or immunologic state upon which they are superimposed, and the responses that are being sampled. The neural or neuroendocrine pathways involved in the behavioral alteration of immune responses are not yet known. Both conditioning and stressor-induced effects have been hypothesized to result from the action of adrenocortical steroids, opioids, and catecholamines, among others. Indeed, all of these have been implicated in the mediation of some immunologic effects observed under some experimental conditions. We assume that different conditioning and stressful environmental circumstances induce different constellations of neuroendocrine responses that constitute the milieu within which ongoing immunologic reactions and the response to immunologic signals occur.(ABSTRACT TRUNCATED AT 400 WORDS)