Effects of repeated stimulation: Habituation

Habituation Learning not to respond to a previously meaningful stimulus The stimulus used to predict something. Now the stimulus loses its predictability and you ignore it Allows efficiency in learning

Habituation Learning not to respond to a previously meaningful stimulus The stimulus used to predict something. Now the stimulus loses its predictability and you ignore it Allows efficiency in learning

Habituation Learning not to respond to a previously meaningful stimulus The stimulus used to predict something. Now the stimulus loses its predictability and you ignore it Allows efficiency in learning

Habituation Learning not to respond to a previously meaningful stimulus The stimulus used to predict something. Now the stimulus loses its predictability and you ignore it Allows efficiency in learning

Habituation Learning not to respond to a previously meaningful stimulus The stimulus used to predict something. Now the stimulus loses its predictability and you ignore it Allows efficiency in learning

Dishabituation When the stimulus changes Signals a change in the situation or setting No longer appropriate to ignore, as changed stimulus may have meaning Why? Something has changed in environment check to see if it is meaningful react to new situation, adapt!

Characteristics of habituation Response decrement: response strength decreases with repeated stimulation. Spontaneous recovery: if the stimulus is withheld and then re- presented, the organism will react to the stimulus Repeated series: with repeated series of exposure, response strength is less ad less Generalization: similar stimuli may exhibit habituation when presented Dishabituation: what has been habituated can be dishabituated

Examples of habituated behavior Salivation responses Visual attention in human infants Startle response in rats Attention to your mother Reaction to fire alarms in college dorms!

Sensitization When aroused, even light stimuli elicit strong reactions Are sensitized: opposite of habituation Over-react to stimuli Over vigilance or hypervigilance When do we see this? Overly hungry/thirst Sexual behaviors Aggression Fear

WHY do we show habituation and sensitization? It is adaptive! Ignore what is irrelevant Attend or hyper-attend to what is important Is habituation and sensitization passive or active learning?

Isn’t this just fatigue or excitement? Is habituation/sensitization the same or different from sensory adaptation or response fatigue? Sensory Adaptation: occurs when you overstimulate a sense system: overuse the receptors; must wait our refractory period Response fatigue: the muscles are tired from responding How is learning to habituate or become sensitized different than this?

Example: Visits to a Nudist Colony when first get there- S (naked people) --> R (lots of blushing) staring behavior decreases over your stay: repeated exposure if leave and come back (repeated series) gets easier with each trip: you adjust faster the more often you leave and come back the more nude bodies- the easier to habituate: Frequency of stimulation might generalize: less embarrassed in locker room, etc. some one comes in with a camera- suddenly embarrassed again - dishabituation

Other Examples: Solomon's research on dogs supports this: Dog presented with series of shocks with repeated presentations of shock, the dog's overt behaviors and heart rate response was smaller however, the after reaction (decrease in heart rate at cessation of shock) was greater it took longer for the heart rate to return to normal

Other Examples: Visual attention in infants Depending on size/complexity of stimulus Infants showed simple habituation to simple visual stimuli But: when shown stimulus again, showed increased sensitization (looked at it more) Drug addiction: will talk about this with classical conditioning Thrill seeking: go from frightened to adrenaline rush then recovery

Context is important Depends on how/when/where stimulus is presented That is, reaction varies depending on context Startle response: Sitting talking with friends Knowing that someone is about to jump out at you and beating them to the “boo” Watching a scary movie A startle will produce different levels of reaction across these settings

Context is important Touch and sexual responses are another good example Touch by a doctor Touch by your mom Touch by your lover All can touch your face, ear, arm, etc., but it is context that regulates how you react to it.

Why habituation and sensitization? Adaptive: Learn what to attend to and ignore Things are more exciting the first time they happen! Can’t attend to everything: need to learn what the important stimuli are Important stimuli change depending on context and experience If don’t learn, die!

What happens physiologicallY? Simple Systems Approach: Eric Kandel Look for similarities in process of habituation across species See strong similarities in terms of behavior Are physiological correlates also similar? Why is this important? If there are strong physiological AND behavioral similarities, suggests that there are generalizable principles and structures that underlie habituation Suggests that this is a very basic and critical type of learning If all organisms show it, must be very robust Must be necessary for survival

The Sea Aplysia A large marine snail Contains only a few thousand neurons so can map the neurons much more easily than larger animal Examine siphon or fleshy spout withdrawal response When you poke the siphon, it withdraws into the snail http://www.youtube.com/watch?v=wE54PPXgstM

Gill-withdrawal reflex Siphon contains 24 sensory neurons that respond to tactile stimulation 6 motor neurons control the gill-withdrawal response Each sensory neuron has a monosynptic connnection Direct connection that involves just one synapse Connects to EACH of the 6 motor neurons Axons from other sensory neurons involved in polysynaptic connections indirect connections mediated by 1 or more interneurons Also connect to these motor neurons

Habituation of the Siphon Stimulate by touching once every minute for 10-15 trials Get habituation within this time Habituation lasts about 1 hour but can extend to 24 hours If continue this stimulation for 3-4 days: long term habituation Lasts several weeks Change in way withdrawal reflex occurs Think of the parameters of habituation: what would you expect?

What is happening to neurons? During habituation: decrease in excitatory conduction always occurs in synapses involving the axons of the sensory neurons NO change in postsynaptic neuron’s sensitivity to the neurotransmitter What changed? Amount of transmitter released by presynaptic (sensory) neurons With repeated stimulation: LESS transmitter released into synapse Similar process found in other animals as well Won Nobel prize for this work!

chemical mechanisms in Habituation? Each time a neuron fires, is an influx of calcium (Ca+) ions into the axon terminals Calcium responsible for release of neurotransmitter Calcium current into axon terminals becomes progressively weaker with repeated stimulation

Why important? Physiological demonstration of learning Later work shows LTP and LTD of axons Able to pinpoint neural changes responsible for habituation Habituation does not necessarily involve long term anatomical changes, but temporary chemical changes Thus appears that learning is flexible: In short term, is likely due to chemical changes For more permanent memories: anatomical changes

Explanation: Opponent Process Theory For every action there is a reaction (wait, isn’t that physics?) Solomon and Corbitt (1974) lots of attention made very "broad"- tried to apply to everything Undermined their own theory

Two (okay 4) effects Primary affective reaction: initially excited by unexpected event- get euphoria from this which will peak: E.g., Think have won the lottery Adaptation phase and steady level: euphoria levels off Peak of after-reaction: a let-down occurs- you were one number off- get "depressed“ Decay of after reaction: return to baseline levels

Church, et al., 1966 Dogs receive 10-s shock while restrained in harness at first- many overt responses freezing escape behaviors pain behaviors at termination of shock: stealthy, hesitant, unfriendly behavior after short time: friendliness reappeared heart rates paralleled these changes

Model Assumes that: For every hedonic reaction (state A) will come opposing reaction (state B) Decline in hedonic value from peak of state A to steady level will result from state B's effect of reducing state A Steady level of hedonic intensity is state A minus state B When stimulus creating state A stops, full force of state B is felt State B slowly decays until hedonic intensity turns to 0

Two main states critically differ: usually are opposite reactions State A develops quickly, closely associated w/intensity of stimulus that produces it when stimulus triggering state A is removed, state A ceases state B develops slowly, produced as reaction to A is slow to decrease, when state A ceases, decays

Effects of Repeated Stimulation repeated presentation of stimulus eliciting state A habituation occurs in state A repeated elicitation of state B strengthens state B and reduces intensity of state A thus: REPEATED presentations of the stimulus that triggered state A will actually lead to a reduction of state A --> because state B increases in intensity that is: w/extended experience: the reaction to the initial stimulus will be smaller than before, but the after reaction will be larger and of longer duration

Critique of Opponent Process Theory Great deal of older research to support the basic phenomenon common criticism: little actual evidence as to actual physiological mechanisms that might correspond to hypothetical a and b states various research shows vastly different time course between examples: immediate to months long

Critique of Opponent Process Theory Several Good aspects of theory as long as emotional responses conform to predictions of theory, not matter whether these are based on single or multiple physiological mechanisms Theory is basically predictive good descriptive model, fairly well supported by research greatest virtue may be its attempt to unite diverse emotional situations into single framework allows for commonalities between emotional responses

Habituation and eating Eating involves repeated presentation of visual, olfactory, gustatory and tactile cues Habituation involves decreases in physiological and behavioral responses to food We eat in food bouts: Begin a bout, often a brief increase in intake rate, followed by a decreasing rate until cessation Time between bouts can vary Presence of other foods Presence of other activities Physiological states: physical and emotional/affective

Habituation and eating What factors affect rate of habituation when eating? Dishabituation: presentation of another food increases eating (but not necessarily for original food) Variety of foods at meal slows habituation Different foods act as novel stimuli inbetween bites of original food Different foods slows habituation to one another Distractors: adding a distractor task slows habituation

Long term habituation Often studied for startle, fear responses Think fire alarms: Repeated presentation with no cause Stop paying attention to fire alarm Generalizes to other settings VERY little research on LTH in humans or even other animals Little evidence that it occurs for eating/food

Affective/emotional/motivational states Classical conditioning is part of eating: associate food with X these are often “motivational” or affective/emotional states Comfort foods: foods associated with comfort Often from childhood Eat to make us emotionally feel better AESOP: affective extension of standard operating procedure assumption that classical conditioning links emotions and food consumption

Habituation and eating! Taking what we know about habituation and applying to food intake (especially in humans). Eat a single food in a meal = faster habituation Distractions reduce rate of habituation Reading Watching tv talking Dishabituation occurs during meals: eatIng another food affects habituation for each food Should we eat 1 food or many foods at a meal? What is the effect of drinking/beverages? In animals: eating bouts followed by drinking bouts Same in humans Does drinking = dishabituation? Does drinking = disruption of eating? Why do bars give out free popcorn and restaurants bring drinks before ordering?

Memory and eating Memory for food is important Do we like this food? Is it familiar? It is rich? Etc…. Differences in individuals for memory for any given food Also individual differences in memory for intake of food Particularly normal body weight and obese Anorexics, bulimic individuals show differences from typical body weight individuals Important factor is sensitization: Food tastes better to some Physical differences: more or fewer taste buds Bodily states Personal experiences

Memory and eating Learning is important part of this memory Clean plate club or not? Individual differences again: Highly sensitized individuals more prone to overeating? Differences in processing of stimulus signals Is over-eating an addiction? Differences in way we react to food Differences in size of DA spike for foods across individuals Some people may be physiologically primed to become “addicted”

Isn’t overeating just sensory specific satiety? Authors argue that eating is more than simple satiety Satiety = full; stop eating because you have had enough Habituation = stop eating because you are “tired of the food” Two are not necessarily related! Habituation model assumes: Hedonic value of one food may influence hedonic value of another food Allows for dishabituation, distraction effects Assumes habituation is a normal nervous system processes Sensory specific satiety only deals with eating and food, not other kinds of stimuli Habituation model assumes that LEARNING is critical factor All the associative stimuli influence intake We eat long after it “tastes good”

Implications of habituation model of eating: We must examine individual differences in Dopaminergic/reward systems Behavioral histories with food Emotional/affective states Unlike in animals, eating for most humans is NOT an energy intake regulation behavior, but a learned behavior We eat because we are Hungry Bored Upset Replacing a thwarted activity It feels good

Good eating practices? Present low fat/healthy food in variety Lots of different kinds of these foods presented at once Encourage low rates of habituation Even encourage disruptors Present high fat/unhealthy food alone Eat alone in absence of disruptions Allow for faster habituation of that food But: don’t assume long term habituation!