Neurobiology of Motivated Behaviours - Lecture 1
Lecture Outline
Course Introduction
Homeostasis and Drives
Homeostasis-like Outcomes
Anticipatory Mechanisms
Setting Points
Allostasis
Intervening Variable Definitions of Drive
Escaping Circularity
Flexible Goals and Affective Displays
Opponent Process Theory
The Hydraulic Drive Model
Drive Reduction and Reward
Beginning of Hedonic Concepts
Incentive Motivation Concepts
Bolles-Bindra-Toates Theory
Alliesthesia
Liking vs. Wanting
Course Introduction
Motivation Concepts
Motivation has been a core explanatory construct in psychology and neuroscience for more than a century because stimulus-response (S-R) models alone cannot adequately explain adaptive behaviour. Even when environmental stimuli remain constant, behaviour varies markedly across time and contexts.
S-R models fall short in explaining adaptive behaviour because:
There is a lack of internal representation (cognition): adaptive behaviour requires an internal model of the environment to evaluate potential outcomes, whereas S-R models rely on fixed associations between inputs and outputs.
Tolman’s rat maze experiments demonstrate that organisms create internal representations of their environments, rather than simply responding to stimuli
Stimulus-response (S-R) models, which posit that behavior is a direct, reflexive reaction to environmental stimuli, cannot fully account for adaptive behavior because they lack the capacity for internal representation, prediction, and flexible re-evaluation of goals. Adaptive behavior requires organisms to anticipate future events, interpret context, and initiate actions to change their environment, rather than just passively reacting to it.
Key reasons S-R models fall short include:
Lack of Internal Representation (Cognition): Adaptive behavior requires an internal model of the environment to evaluate potential outcomes, whereas S-R models rely on fixed associations between inputs and outputs.
No Future Prediction: Adaptation involves planning based on future predictions, while S-R models are purely reactive, focusing only on immediate input.
Inflexibility to Context Changes: S-R models struggle to adjust when the relationship between an action and its outcome changes (e.g., if a previously rewarded action no longer works).
Passive vs. Active Nature: S-R models assume organisms wait for a stimulus, whereas adaptive agents often actively seek stimuli or initiate actions to change their environment.
Failure to Account for Volatility: In rapidly changing or "volatile" environments, S-R models are too slow to update, whereas adaptive systems adjust to changing reward probabilities.
Conversely, when organisms are pursuing goals or avoiding threats, behaviour often becomes highly stable, persistent, and directionally organized. Motivation concepts were introduced to resolve this apparent contradiction.
At a functional level, motivation refers to internal processes that regulate the selection, vigor, persistence, and direction of behaviour as a function of biological needs, learned values, and current internal states. These processes operate upstream of motor output and perceptual processing, biasing how organisms interact with their environment.
Motivation concepts have been considered necessary for over 100 years. They are needed to explain two features of behaviour:
1 - Variability of behaviour over time when facing a constant stimuli
“Why do individuals choose to do different things at different times?”
2 - Short-term stability and directedness of behaviour when obtaining goals or avoiding threats
“Why do individuals seek out specific things at particular times?”
“Why do they react as they do to affectively important stimuli encountered on the way"?”
Homeostasis & Drives
Homeostasis: Maintenance of a stable internal state.
Coined by Walter Cannon in 1925.
Typically refers to a regulatory system that uses a setpoint to maintain a stable physiological state.
Components of Homeostasis:
Setpoint: Can be a single optimum level or narrow range.
Error Detector: Measures the actual physiological state to decide if a deficit exists.
Error Correction Mechanism: Activates appropriate responses that provide negative feedback to correct the deficit and return physiological state to the setpoint (e.g., eating when hungry).
Important task: Avoiding error states, as deviation out of range can be dangerous (e.g., body water level, neuronal glucose level, nutrient storage). Error detection prompts corrective responses to bring levels back into range.
Homeostatic motivation applies not only to hunger but also to sex, aggression, and other motivations, implying models impose triggers based on deviations such as high levels of sex hormones.
Homeostasis-Like Outcomes
Debate exists over whether brain mechanisms of motivation are truly homeostatic.
Motivational mechanisms can maintain stability through:
Anticipatory mechanisms
Settling points, instead of setpoints.
Anticipatory Motivation
Anticipatory behaviours: Initiate motivated behaviour before a deficit occurs (e.g., anticipatory drinking or eating).
Can be elicited as a classically conditioned response or other pre-emptive mechanism prior to depletion.
Appears homeostatic as it maintains stable physiological states long-term without any physiological deficit, potentially creating a temporary surplus.
This process can still activate homeostatic brain systems and be triggered by predictive cues or actual physiological depletion.
Settling Points
Defined as a stable state caused by a balance of opposing forces without any setpoint or error detection.
Though stable, settling points can change if the balance of opposing forces alters.
Homeostatic motivations may reflect physiological settings among opposing neural-hormonal-behavioural systems (e.g., hunger may not have a homeostatic mechanism).
Settling Point Theory of Hunger (Bolles): No body weight setpoint exists. Instead, body weight has a moderately stable settling point determined by internal appetite and satiety mechanisms along with external availability and palatability of food. Rising obesity rates reflect changes in external conditions rather than altered brain setpoints.
Allostasis
Related to homeostasis; refers to the physiological regulation of changed states, often involving positive feedback responses.
Initial responses contribute to larger later responses in a snowball effect (e.g., neuroendocrine reactions to stress).
Allostasis explains regulations that change over time while keeping the appearance of homeostasis through negative feedback responses (e.g., addiction management).
Described as “fluctuating homeostasis,” chasing a moving settling point.
Intervening Variable Definitions
Drive does not have to be defined exclusively as homeostasis; its original purpose was to explain and predict behaviour.
Drives provide homeostatic explanations for motivated behaviour and are also useful for efficient causal descriptions and predictions.
Drives are most valuable in their minimal form as intervening variables.
Example: The use of “thirst drive” simplifies the S-R (stimulus-response) relationships in motivation, as motivation cannot be directly observed but can be measured through its correlated effects on behavioural dependent variables.
Escaping Circularity
A concern about motivational explanations is the potential for circular explanations—explaining an observation in terms of itself.
To escape circularity, drives (or other concepts) must lead to new predictions rather than restating previous observations.
A worry arises that drive increases behaviours, but the variability in responses complicates determining which behaviour accurately reflects drive.
Flexible Goals, Affective Displays
An intervening variable represents only the most minimal concept of motivation.
To avoid oversimplification, minimum criteria for defining "real" motivation has been suggested, emphasizing that drive alone does not qualify motivation.
Teitelbaum’s Flexible Goals: Real motivation must promote flexible instrumental behaviour. Organisms must be able to learn new operant responses to achieve goals, building on earlier proposals by Craig and Sherrington.
Craig’s Sequential Phases
Proposed that all motivated behaviour can be divided into two sequential phases:
Appetitive phase: Flexible approach behaviour before the motivational goal is found; flexibility aids in finding the goal.
Consummatory phase: Triggered by goal stimulus, consummates/terminates the appetitive phase—allowing the organism to interact with the sought-after goal.
Teitelbaum’s Definition of Motivation
Emphasizes the appetitive phase as crucial; it is insufficient to merely display consummatory behaviour or modulate it via homeostatic drives.
Flexible appetitive behaviour must interact with instrumental associative learning to develop new responses.
Epstein’s Additional Criteria
Proposed three additional criteria to distinguish truly motivated behaviour:
Flexible goal-directedness
Goal expectation
Affect
Flexible goal-directedness builds upon Teitelbaum’s operant learning concept, demonstrating behaviourally that the target was indeed a true goal.
Goal Expectation
A component of motivation responsible for behaviour in everyday human life.
Can take declarative forms and may include forms of associative learning that anticipate the goal without cognitive expectation (e.g., classical conditioning). Evidence for goal expectation includes the incentive contrast effect observed even in rat behaviour.
Affective Reactions
Epstein noted that real motivation is accompanied by affective reactions to the goal itself.
Behavioural, autonomic, or physiological responses indicate the presence of some hedonic or emotional state.
Motivation directed towards hedonic goals elicits affective reactions, confirming the behaviour was motivated.
Opponent Process Theory
Proposed by Solomon, suggesting that drives involve affectively valenced stimuli (pleasant or unpleasant).
All hedonic stimuli activate not only their direct hedonic reaction in the brain but also an opponent process of opposite hedonic valence; this requires stimuli to be strong and prolonged.
a-process: The initial response to the stimulus, typically triggers the b-process.
b-process: Generates an opposite hedonic response.
Underlying assumption: Neurophysiological mechanisms in motivation are tuned to achieve stability (homeostasis).
Opponent Process Theory and Heroin Tolerance
a-process: Brain reward circuits activated by the drug produce positive affective reaction (A-state).
b-process: A physiological counteraction occurs to the a-process, which, if experienced alone, would be unpleasant (B-state).
Tolerance results from a reduction in A-state, reflected as diminished pleasure from heroin over time.
Notably, only the b-process's intensity increases with repeated exposure to the drug.
Other Points and Limitations of OPT
For unpleasant stimuli, the opposite process of the theory works in reverse.
Classical conditioning may stimulate opponent processes without requiring the a-process, as seen in the phenomena surrounding tolerance.
Koob proposed specific neural mechanisms for mediating the b-process, especially in drug addiction—specifically involving down-regulation in the mesolimbic dopamine system.
Limitations: b-process effects may not always emerge with every a-process event. Even when they do occur, the b-process is not always the primary motivating factor behind behaviour; other influences, such as addiction, may drive continued substance use despite withdrawal b-processes.
Hydraulic Drive Model
The hydraulic drive model metaphorically describes motivation as pressure building in a fluid reservoir until it bursts through an outlet, thus being expressed as behaviour.
In Lorenz’s model, internal causes of a motivational drive (e.g., hormonal production) fill the reservoir, while external motivational stimuli (e.g., the availability of food) act to open its outlet.
Interaction between Internal and External Forces:
The strength of internal drive interacts with the strength of external stimuli; as internal drive increases, less external stimulus strength is needed to elicit motivated behaviour.
Conversely, if internal drive is low, more external stimuli are required to trigger motivated behaviour.
A significant scenario in high internal drive states is that motivation can erupt without external stimuli, known as a vacuum reaction as theorized by Lorenz.
Limitations of the Hydraulic Model
It inaccurately portrays most motivated behaviours as eruptions; while some may experience this (e.g., canary nest-building drive), many do not.
Behavioural expressions of motivation often do not reduce motivation; they tend to prime or enhance subsequent intensity (e.g., the cocktail peanut phenomenon).
Priming is highly observable in studies where animals receive drug and brain stimulation rewards. These phenomena are better explained through incentive motivation concepts.
Usefulness of the Hydraulic Model
Despite limited adoption among behavioural neuroscientists due to insufficient details about neural mechanisms, it can be useful to compare against behavioural observations regarding:
The temporal buildup of motivation.
The effects of preventing behavioural expression.
The interaction between internal motivational factors and external stimuli in regulating motivated behaviour.
Drive Reduction & Reward
Historically, drive reduction has been viewed as the chief mechanism of reward. For instance, food is considered a reward because it reduces hunger drive, but this perspective is flawed.
Evidence Against Drive Reduction as Chief Mechanism of Reward:
Reducing physiological drive through methods like intravenous administration does not stop eating.
Anecdotal examples (e.g., Tom) and animal evidence support this claim (e.g., studying dogs).
Brain stimulation reward (BSR) studies revealed that predictions based on drive reduction often yielded incorrect outcomes; in fact, numerous instances showed that reward functions as an independent motivational phenomenon, suggesting that drive reduction is not the primary driver behind reward.
Beginning of Hedonic Concepts
The predominant idea within many incentive motivation theories centers around the concept of hedonic reward, which can cause significant behavioral changes.
Hedge products and rewards can overturn previously established habits (e.g., pure sensory rewards showing that conditioned stimuli can reinforce behaviour even without reducing drives).
Example: Rats consume saccharin, which has no nutritional value but presents pleasure.
Neural Encoding of Hedonic Sensations: Pfaffman argued that the neural encoding of hedonic sensations itself must be rewarding and motivates behaviour independently of drive reduction.
Incentive Motivation Concepts: The works of Stellar further expanded on these ideas, leading to developments in incentive motivation spanning the 1960s, highlighting the Bolles-Bindra-Toates theory.
Bolles-Bindra-Toates Theory
Proposed by Bolles, suggesting organisms are driven by incentive expectancies rather than solely by drives or drive reduction. These are learned expectations of a hedonic reward, called S-S* associations—where a neutral stimulus (S) becomes associated with a hedonic reward (S*).
It underlines that the S* possesses motivational value prior to learning while S does not, and learning results in a predictive expectancy of reward.
Bindra, however, challenges Bolles’ concept by rejecting the idea that expectation is the most significant motivational factor; rather, he suggests that a conditioned stimulus (CS) evokes the same motivational state normally induced by the reward itself due to classical conditioning, making the CS equivalent to the S*.
Critique of Bolles-Bindra Theory
Critics of Bindra suggest that, should CS simply transform into persistent incentives via learning, there should be constant responses to them as incentives regardless of the organism’s drive state.
This indicates that physiological drive states influence motivation even when drive is not equated to it.
Interaction of Physiological Drive States
Toates posits that physiological depletion states may enhance the incentive value of goal stimuli (S*).
These depletion states do not directly drive motivated behaviour but amplify the hedonic impact and incentive value of the actual reward.
Physiological signals can elevate the hedonic/incentive value of conditioned stimuli (CS), resulting in a three-way interaction between physiological deficit, the stimulus, and its learned association with the unconditioned stimulus (UCS).
Alliesthesia
Alliesthesia represents a change in sensation; the pleasure derived from hedonic incentives can be influenced by relevant physiological drive states (e.g., hunger may intensify pleasure perception from sugar).
Toates argues that physiological drive states modulate the incentive and hedonic value of associated rewards and their predictive cues, aiding in the view that conditioned motivation could follow incentive rules but maintain modulation through internal states.
Liking vs. Wanting
The Bindra-Toates incentive concepts suggest that learnt Pavlovian incentive stimuli are experienced as both “liked” and “wanted” due to the processes of reward learning.
Berridge & Robinson’s Distinction: Proposes a split can occur between the liking and wanting incentive processes due to distinct underlying brain mechanisms, resulting in the incentive salience model.
Conclusion
The fundamental concepts discussed here provide a robust foundation for understanding the neurobiological underpinnings of motivated behaviours—a critical area of study in the field of neurobiology and psychology, setting the stage for subsequent lectures that will delve deeper into the dynamics of pleasure and motivation in psychological and physiological contexts.