Biological psychology manipulates and observes psychological variables just as do all other fields of psychology. However, to delineate the somatic contribution to behavior and mental functions, biological psychology needs to draw evidence from studies combining methods of psychology with those of other disciplines such as neuroscience, pharmacology, immunology, and endocrinology. These methods allow the investigator to probe into relevant bodily systems. In contrast to many other fields of psychology that focus their research mainly on human beings, biological psychology investigates both human and nonhuman species. Study of animal subjects is justified for two reasons. First of all, from an evolutionary perspective, the bodily systems sub serving mental activity, like any other biological features, are under the pressure of natural selection and have evolved over a long period of time as a consequence of adaptation to the environment. Common components may underlie mental functions of both humans and other species in terms of their structural bases or operational mechanisms. Investigating the brain function of animals can therefore contribute significantly to our understanding of that of humans. This expectation is substantiated by numerous findings suggesting shared biological bases of human and nonhuman behavior.
[...] Studies in biological psychology may also adopt the correlational approach in which behavioral and somatic variables are measured simultaneously in each of a group of subjects, so that the extent to which the two measures co-vary can be measured. For example, the neurophysiological activity of a specific structure may correlate with behavioral performance during acquisition in a new learning task. In another case, the level of androgen or glucocorticoid may correlate with the social hierarchical status of monkeys in a colony. [...]
[...] However, this by no means reduces its importance in biological psychology research, because the presence of a correlation between two measures suggests future intervention studies, and lack of correlation may help to limit the domain for further investigation. Even when a causal relationship between two variables has been established, correlational studies still provide additional information. Based on the evidence that disrupting the function of a somatic structure alters a specific type of behavior, one can conclude that the somatic structure exerts critical influence on that behavior, but there is no guarantee that the structure is normally engaged when the behavior is performed in nature. [...]
[...] The nature of neural coding for mental features has been an issue fundamental to research in biological psychology. The so-called ‘single neuron doctrine' suggests that activity of single neurons is capable of forming unitary mental representations, whereas other theories insist that representation of mental activity relies on ensembles of neurons. While both views have strength and weakness in guiding research and interpreting findings, the results give one of the best examples that traits of behavior (direction of movement in this case) are represented by collective activities in a population of neurons. [...]
[...] Another major concern in methodology is how to choose, from a whole array of available techniques, the appropriate ones that can detect or affect the relevant somatic events, which vary tremendously in both the spatial and temporal dimensions. The basic structural and functional unit of the nervous system is the neuron. Yet mental activity may be related to episodes occurring at subordinate levels, such as the synapse, intra- cellular organelles, and specific molecules, or at super ordinate levels such as neural networks, maps, systems, or even the entire CNS. [...]
[...] To students in biological psychology, the most challenging question concerning the study of the motor system is how the brain transfers emotion, motivation, visual signals, verbal instructions, as well as self-generated thoughts including plans, intention, and will into motor behavior. Recent evidence begins to address this issue, yet the picture is far from clear. In rats and cats, the midbrain periaqueductal gray (PAG) appears to mediate some reactions elicited by emotional stimuli. Part of its input derives from the limbic cortex, hypothalamus, and amygdala, all of which are implicated in emotional functions. [...]
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