Biology 312: January 5, 1999



Biology 312: February 7, 2003

Development of Behavior/Critical Periods

I. Development of behavior: Overview

A. Physiological/morphological aspects of behavioral development

1. Nervous system development

2. Changes in non-neuronal morphology

3. Changes in hormonal state

B. Role of experience

II. Development of bird song

A. Basics of bird song.

1. Why do birds sing

2. How many songs does an individual sing?

a) Possible adaptive value of different song types?

B. Why study development of bird song?

1. Like the cricket call, bird song has clearly identifiable acoustic elements

2. Songs are species-specific

3. Behaviorally, clear steps in the development of bird song.

4. Neural circuitry underlying song is concurrently being examined, so we can look at relationship between brain and behavior

C. Physiological aspects of song (Zebra finch)

1. Sexual differences in neuroanatomy

a) Nine brain areas (primarily forebrain) are apparently responsible for song production.

• Larger regions in males

• More/larger neurons

2. Genetic differences between males and females (XX vs. XY) cause differences in hormones which affect brain development in embryo (organizational effects), as well as turn on singing in adulthood (activational effects.)

a) Male birds are XX (reverse of mammals); lack of Y-chromosome causes production of estrogen, which stimulates growth/development of song regions

b) Elevated testosterone in adult males is necessary to "turn on" singing

c) Females given both estrogen during the critical period (just at hatching) as well as testosterone as adults will sing. Neither alone is sufficient to induce singing.

D. Role of learning in song development (white-crowned sparrow)

1. SENSORY PHASE: Acquisition and storage

2. SENSORY-MOTOR PHASE: Retrieval, production, stabilization

3. Choice of tutor: contradictory evidence from zebra finsh studies

a) Bohner and Clayton

b) Williams

III. Critical periods

A. Original definition: A brief, well-defined developmental period when an organism becomes impressionable to certain "environmental" stimuli. Exposure to particular stimuli at this time produces irreversible effects on subsequent behavior. (Konrad Lorenz)

1. Some modification of this strict definition:

2. Timing of critical period: usually early in life

B. Role of hormones during critical periods

1. A hormone can itself be the stimulus (internal regulation)

2. A hormone can mediate the response of the organism to some external environmental cue.

C. The classic example of imprinting: filial imprinting in goslings/ducklings. What does it tell us about the mechanisms of imprinting/learning?

1. Being born with a particular behavior does not mean the behavior is "innate" or genetically programmed, since critical periods for imprinting can occur within embryos.

a) First set of experiments (Gottlieb, 1965): Trying to distinguish whether important cues were visual or auditory

b) Second set of experiments (Gottlieb, 1978): Trying to determine whether auditory recognition is innate or learned

• These experiments also determined critical period

c) Implications for humans?

2. Imprinting is complex: more than one cue and critical period for the compete development of a particular behavior.

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