Lecture 5

Proximate and Ultimate Questions About Behavior

Proximate Questions

  • What causes the behavior to be expressed?
    • Mechanical stimulation (touch) on body (particularly behind head).
    • Activity in a neural circuit that inhibits side-to-side head movements during reversing.
    • This is influenced by genes coding for neural activity.
  • What causes the behavior to develop in individuals?
    • Innate behavior is genetically mediated, implying a biological basis for behavior development.

Ultimate Questions

  • How is the behavior useful to the individual?
    • This behavior, once expressed, allows the individual to escape from a ring trap created by predatory fungi by backing out before the trap closes.
    • Location specificity is critical to avoid false negatives (i.e., mistaking the absence of a threat).
  • How was the evolution of the behavior being researched?
    • Researchers studied natural mutants and selectively analyzed genes to observe changes in behavioral expression.
    • Investigated escape success and differential survival rates among individuals.

Modulation of Behavior

Intended Learning Outcomes

  • Explain how behavior can be modified by changes in the nervous system activity (e.g., Aplysia example).
  • Discuss and illustrate proximate current causes of altered nervous system activity and behavior.
  • Discuss proximate historical causes of altered nervous system activity in the context of the development and ontogeny of behavior.

Neural Activity and Behavior

  • Changes in neural activity are directly linked to modified behavior.
    • Behavior is influenced by the balance of excitatory and inhibitory neuron inputs.
    • Interneurons are crucial for providing behavioral flexibility, exemplified by the sensitization of the gill-withdrawal reflex.

Gill-Withdrawal Reflex

Circuit Components

  • Circuit Components:
    • Skin of siphon → Sensory neuron → Interneurons → Motor neuron → Gill

Thresholds for Activation

  • High Threshold:
    • Strong stimulus needed to elicit a response leading to lower behavior expression probability.
  • Low Threshold:
    • Weaker stimulus eliciting a behavior leads to a higher probability of expression.

Proximate Current Causes of Behavior Modulation

  1. Stimulus
  2. Other Relevant Information
    • Behavior of other animals, memory, and emotional states (fear, hunger).
    • Physiological state (e.g., sickness).
  3. Current State of Nervous System
    • Individual's genetic makeup (baseline thresholds).
    • Environmental factors (e.g., photoperiod leading to hormonal changes).
    • Pharmacological influences.

Hormonal Influence on Behavior

  • Hormones can modify thresholds for behavior expression based on:
    • Time of day, year (e.g., breeding seasons), and lifetime stages (puberty, menopause).
    • Presence of certain stimuli/events (competition, threats) enhances behavioral adaptability.

Hormonal Impact on Neural Circuits

Components Affected by Hormones

  • Hormones affect three main circuit components:
    • Input (sensory systems)
    • Central processor (central nervous system)
    • Output (effectors leading to behavior)

Example: Bird Song Circuit

  • Components:
    • HVC, RA, Area X, POM (DLM), nXIIts
    • Testosterone impacts song stereotypy and variability.

Proximate Historical Causes of Behavior Modulation

  • Genetic and Environmental Influences:
    • Hormonal environments during development can influence nervous system structure.
    • External factors, such as learning experiences, impact the individual's developmental trajectory.

Key Examples

Example A: Bird Song and Hormones

  • Some songbirds exhibit sexually dimorphic singing patterns influenced by developmental hormonal exposure.
    • High testosterone levels during development lead to larger neurons and nuclei in song circuits.

Example B: Bird Song and Social Learning

  • Some songbirds require exposure to conspecific songs to exhibit appropriate singing behavior.
    • Social environments facilitate necessary learning for song development.

Ultimate Causes of Behavior Modulation

  • Proximate causes evolve over time leading to the development of specialized nervous system structures.
    • This includes the evolution of sensory receptors, responsiveness in the central nervous system, motor patterns, and hormone receptors on neurons.