Neurophysiological approaches

Whether any of the neurophysiological approaches is more or less sensitive than psychological instruments to delineate drug effects in healthy volunteers is difficult to judge because only a few studies used both types of methodology in parallel. Nevertheless, in order to provide a rough overview, Table 3.9 sets out... 

Baribeau, J., Laurent, J.-P., Decary, A. (1993, September). Tardive dyskinesia and associated cognitive disorders A convergent neuropsychological and neurophysiological approach. Brain and Cognition, 23, 40-55. 

Adams, R. N., 1978, In vivo electrochemical recording—a new neurophysiological approach,... 

Some of the best evidence of links between effects at different organizational levels comes from studies with OPs, where levels of AChE inhibition have been compared with associated neurophysiological and behavioral effects. In adopting this approach, however, the picture is complicated by mounting evidence for these compounds acting on target sites other than AChE, as discussed in Section 16.3. Thus, behavioral disturbances caused by an OP may be the outcome of interaction with both AChE and one or more other sites of action. The following account, however, will be concerned with situations where effects of OPs are closely related to levels of AChE inhibition. More complex scenarios will be discussed in the next section. 

The causal approach is undeveloped. Fear is the only emotion we are dose to understanding at the neurophysiological level (LeDoux 19%). We do not know if other emotions have similar neural pathways. The relation between, say, parental love and fear may turn out to be like the relation between whales and sharks. Because of our lack of understanding of the core emotions, we should keep an open mind about the borderline cases. When more is known about the neurobiological substrates, some of the marginal cases may move to the center, and vice versa. 

I emphasize a psychological approach to states of consciousness because that is the approach I know best, and I believe it is adequate for building a comprehensive science of consciousness, but because the approach deals with systems, it can be easily translated into behavioral or neurophysiological terms. 

The primary approach currently used to detect and characterize potential neurotoxicants involves the use of animal models, particularly rodents. Behavioral and neurophysiological tests, often similar to the ones used in humans, are typically administered. The sensitivity of these measures to neurotoxicant exposure is widely accepted. Although it is often not possible to test toxicant effects on some higher behavioral functions in animals (e.g., verbal ability, cognitive flexibility), there are other neurobehavioral outcomes such as memory loss, motivational defects, somatosensory deficits, and motor dysfunction that can be successfully modeled in rodents. These behaviors are based on the ability of the nervous system to integrate multiple inputs and outputs, thus they cannot be modeled adequately in vitro. Although the bulk of neurotoxicity data has been collected in rodents, birds and primates are also used to model human behavioral outcomes. 

Cone snails, Conus spp., have been investigated because of their production of conotoxin peptides. From an evolutionary standpoint, the production of conotoxins is quite interesting due to their wide range of neurophysiological activities. The conotoxins are small peptides, 10-30 amino acids, with conformations constrained by multiple disulfide bonds that target a number of receptors in vertebrate and invertebrate nervous systems. Cone snails use these toxins to immobilize prey, which allows the relatively slow-moving cone snails to feed on fish and worms. The wide variety of conotoxins isolated and the hypervariability within peptide sequences has led some to hypothesize a combinatorial biosynthetic approach for the production of conotoxins.116117... 

Clearly, these are preliminary findings that need to be confirmed, extended by genome-wide association study, and examined with regard to the neurophysiological underpinnings. For the latter approach, the importance of OT-related signaling... 

Model-Based Approaches to Control Adaptive Clitics Neurophysiologically Based Approaches... 

One approach to incorporating a stronger neurophysiological foundation has been to utilize an architecture for the overall control system that is based upon neurophysiological models, that is, mimicking the neurophysiological system at a block diagram level. This type of approach has led to the development of hierarchical control systems that are based upon the hierarchical structure of the human motor control system [Kawato et al, 1987 Srinivasan et al., 1992]. 

A biomedical control system that utilizes a neurophysiologically-based approach has been developed for use in Functional Neuromuscular Stimulation (FNS) systems [Abbas, 1995 Abbas and Chizeck, 1995). FNS is a rehabilitation engineering technique that uses computer-controlled electrical stimuli to activate paralyzed muscle. The task of a control system is to determine appropriate stimulation levels to generate a given movement or posture. The neural network control system utilizes a block diagram structure that is based on hierarchical models of the locomotor control system. It also utilizes a heterogenous network of neurons, some of which are capable of endogenous oscillation. This network has been shown to provide rapid adaptation of the control system parameters [Abbas and Chizeck, 1995 Abbas and Triolo, 1997] and has been shown to exhibit modulation of reflex responses [Abbas, 1995]. 

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