Ingestive Behavior Notes

Basic Instincts/Drives in Humans

  • Humans have evolved basic instincts/drives, which have been conserved through evolution:

    • Fighting

    • Fleeing

    • Mating

    • Feeding (eating)

Theories Explaining Food Motivation

  • Drive Reduction Theory:

    • We eat due to internal physiological needs (e.g., energy deficits, such as during fasting).

  • Positive Incentive Theory:

    • We eat in response to the anticipated pleasure derived from food (e.g., the thought, sight, or smell of food).

Neural Systems in Ingestive Behavior

  • Ingestive behavior is regulated by complex neural systems:

    • Homeostatic Regulators:

    • Hypothalamus

    • Brainstem

    • Non-homeostatic Regulators:

    • Cortex: Involved in decision-making.

    • Basal Ganglia: Associated with motor movements, learning, and emotion.

    • Limbic System: Engages in emotion and memory processing.

  • Three distinct phases of ingestive behavior:

    • Preparatory Behavior

    • Consummatory Behavior

    • Post-Consummatory Behavior

Preparatory Phase

  • Initiation Phase:

    • Shifts attention to food; decision-making based on prior experiences and effort perceptions.

    • Positive outcomes associated with eating increase motivation to seek food.

  • Procurement Phase:

    • Involves planning and foraging for food after deciding to eat.

    • Actions driven by the expected pleasure or satisfaction from food.

  • Energy Deficit and Hedonic Evaluation:

    • Energy deficit triggers hunger and the desire to eat.

    • Anticipation of pleasure during the search for food enhances motivation to eat.

Hormonal Influences on Eating Behavior

  • Leptin:

    • A hormone produced by fat cells, regulating hunger and energy balance.

    • High leptin levels signal fullness; low levels signal hunger.

  • Olfaction (Sense of Smell):

    • Detects food scents, triggering feelings of hunger or craving.

  • Ghrelin:

    • Known as the "hunger hormone"; rises when hungry and induces foraging behavior.

Consummatory Phase

  • The stage of actually eating and enjoying food.

    • Direct Pleasure from Smell and Taste:

    • Sensory experiences provide pleasure during consumption.

    • Satiation Signals:

    • Consumption continues until the body signals fullness (satiation).

    • Different foods have varied lengths of ingestion (e.g., hamburger: few minutes; steak: 10-20 minutes).

    • Longer Eating Time = More Enjoyment:

    • Longer meals can enhance satisfaction due to extensive reward processes interacting with enjoyment.

Post-Consummatory Phase

  • Begins after finishing eating and lasts until there is a need to eat again.

    • Starts at Meal End:

    • Ends when the next eating occasion emerges.

    • Nutrient Sensors and Food Reward:

    • Special sensors in the body generate feelings of satisfaction and fullness post-eating.

    • Taste Not Required for Food Reward:

    • Nutrients alone can trigger satisfaction, irrespective of taste detection (e.g., studies on mice lacking certain taste receptors).

Emotional and Sensory Influences

  • Sensory stimuli and emotional states reinforce the rewarding experience of eating food.

  • These experiences can adjust the hedonic evaluation and reward expectancy for future eating behaviors.

  • This influences the probability of eating the same food later and immediate food choices.