Читать книгу The Behavior of Animals - Группа авторов - Страница 76

Hormones are substances released by endocrine glands into the bloodstream; many of them are known to have behavioral effects. Lashley (1938) suggested that hormones could affect behavior in at least four different ways: during the development of the nervous system, by effects on peripheral structures through alteration of their sensitivity to stimuli, by effects on specific parts of the central nervous system (central behavior mechanisms), and by nonspecific central effects. Abundant evidence for all these modes of action has accumulated since Lashley’s time, although the mechanisms by which hormones influence behavior have turned out to be more complex and diverse than early investigators realized (Beach 1948).

Both peripheral and central effects of the hormone prolactin are seen, for example, in the parental feeding behavior of the ring dove. Prolactin is responsible for the production of crop “milk” sloughed-off cells from the lining of the crop that are regurgitated to feed young squabs. Lehrman (1955) hypothesized that sensory stimuli from the enlarged crop might induce the parent dove to approach the squab and regurgitate. His experiments showed that local anesthesia of the crop region, which removes the sensory input, reduced the probability that the parents will feed their young. More recent experiments have confirmed that prolactin has both peripheral and central effects on the dove’s parental behavior (Buntin 1996).

The maternal behavior of the rat provides an example that illustrates the variety of hormonal effects. The hormones released at parturition change the dam’s olfactory sensitivity to pup odors, reduce her fear of the pups, and facilitate learning about pup characteristics; they also activate a part of the brain essential for the full expression of maternal behavior (see Fleming & Blass 1994). More extensive coverage of the relation between hormones and behavior can be found in Chapter 6.

Substances released from the neuron terminals into the synapse are known as transmitters; many of these are known to be involved in activating specific behavior systems such as feeding and drinking (see Nelson 2016). Transmitters such as dopamine are thought to mediate the motivational effects of stimuli for a wide range of behavior systems, especially their reinforcing effects (Glimcher 2011). Examples of these effects are given in Chapter 6. Psychoactive drugs, which are thought to exert their effects by altering neurotransmitter functioning in the brain, are also causal factors for behavior, but will not be considered further here.