2.4. Time Frame of Hormonal Action:
Organizational and Activational Effects
The impact of hormones on a biological system depends on the timing of
exposure. Within a defined period during development, the critical or sensitive period, hormones can exert dramatic and irreversible (organizational)
effects by regulating the growth of the CNS and somatic tissues and can
permanently modify the function of the system. Hormones released during
adulthood usually induce transient changes on a much smaller scale (activational) that are reversible (Phoenix et al. 1959). Although the distinction
between organizational and activational effects is not always clear-cut
(Arnold and Breedlove 1985), the two categories are particularly useful
when describing the hormonal regulation of sexual differentiation of the
nervous system and the behavior of animals. For example, steroid hormones
play a critical organizational role in differentiating the physiology and morphology of male and female vertebrates during development and later play
an activational role in eliciting male- and female-typical patterns of reproductive behavior in adulthood. In this chapter, major emphasis will be
placed on activational effects of hormones reflecting the volume of research
in the field. Organizational effects of hormones will be discussed in the
section on sexually differentiated vocal production.
2.5. Physiological Substrates for Acoustic
Communication Are Targets for Hormones
Acoustic communication systems present useful models for investigating
the action of hormones on behavior. In these systems, the key elements
include the sound-production apparatus used by the communicator or
sender and the auditory apparatus of the receiver. Sound production is
driven by central nervous system elements that include motor neurons and
their afferents. Sound reception includes cells of the inner ear and CNS
nuclei involved in decoding acoustic information. Many of these elements
have been shown to express receptors for hormones; examples include forebrain vocal centers in songbirds, the auditory midbrain, vocal organ, and
motor neurons of frogs. Thus, vocal neuroeffectors in both the CNS and the
periphery can be direct targets of circulating hormones.
3. Activational Effects of Hormones on
Acoustic Signal Production
Animals typically vocalize when they are in a particular physiological state.
For example, sexually active males produce courtship vocalizations to
attract females for successful reproduction. Thus, the internal endocrine
6. Hormonal Control of Communication
283
Organizational and Activational Effects
The impact of hormones on a biological system depends on the timing of
exposure. Within a defined period during development, the critical or sensitive period, hormones can exert dramatic and irreversible (organizational)
effects by regulating the growth of the CNS and somatic tissues and can
permanently modify the function of the system. Hormones released during
adulthood usually induce transient changes on a much smaller scale (activational) that are reversible (Phoenix et al. 1959). Although the distinction
between organizational and activational effects is not always clear-cut
(Arnold and Breedlove 1985), the two categories are particularly useful
when describing the hormonal regulation of sexual differentiation of the
nervous system and the behavior of animals. For example, steroid hormones
play a critical organizational role in differentiating the physiology and morphology of male and female vertebrates during development and later play
an activational role in eliciting male- and female-typical patterns of reproductive behavior in adulthood. In this chapter, major emphasis will be
placed on activational effects of hormones reflecting the volume of research
in the field. Organizational effects of hormones will be discussed in the
section on sexually differentiated vocal production.
2.5. Physiological Substrates for Acoustic
Communication Are Targets for Hormones
Acoustic communication systems present useful models for investigating
the action of hormones on behavior. In these systems, the key elements
include the sound-production apparatus used by the communicator or
sender and the auditory apparatus of the receiver. Sound production is
driven by central nervous system elements that include motor neurons and
their afferents. Sound reception includes cells of the inner ear and CNS
nuclei involved in decoding acoustic information. Many of these elements
have been shown to express receptors for hormones; examples include forebrain vocal centers in songbirds, the auditory midbrain, vocal organ, and
motor neurons of frogs. Thus, vocal neuroeffectors in both the CNS and the
periphery can be direct targets of circulating hormones.
3. Activational Effects of Hormones on
Acoustic Signal Production
Animals typically vocalize when they are in a particular physiological state.
For example, sexually active males produce courtship vocalizations to
attract females for successful reproduction. Thus, the internal endocrine
6. Hormonal Control of Communication
283