Reward ppt

Biol2052 Neuroscience

  • Focus: Complex brain functions related to pleasure, reward, and food.

  • Instructor: James Dillon (jcd@soton.ac.uk)

Learning Outcomes

  • Key competencies to demonstrate:

    • Describe components of reward: hedonic vs motivational aspects.

    • Identify brain structures involved in the rewarding effects of food.

    • Explain neural substrates related to different reward components.

Introduction to Pleasure and Food Reward

  • Overview of:

    • Pleasure derived from food and its impact on feeding behavior.

    • Increase in the prevalence of eating disorders.

    • Key brain structures coordinating feeding and the distinction between homeostatic and reward circuits.

    • Insights into eating disorders and their neural basis.

Epicurus' Perspective on Pleasure

  • Quote: “We recognize pleasure as the first good innate in us…”

  • Importance of pleasure in guiding future behavior choices related to food intake.

  • Eating pleasurable foods reinforces the desire to repeat the behavior.

Importance of Eating

  • Eating is vital for survival and maintaining homeostasis.

  • Pleasurable effects of food can drive consumption beyond metabolic needs.

  • Hedonic circuits ('liking') play a crucial role in the pleasurable experience of eating.

Eating and Reward Components

  • 'LIKING'

    • Represents pleasure associated with food consumption.

  • 'WANTING'

    • Motivational drive to seek food.

  • Both components contribute to the overall reward experience of eating.

Overview of Eating Disorders

  • Types include obesity, bulimia, and anorexia.

  • Severe obesity rates have nearly doubled among children in the past decade.

  • Understanding neural mechanisms behind food reward can lead to new therapeutic approaches.

Brain Systems Controlling Food Intake

  • Homeostatic System:

    • Orexigenic: Increases appetite.

    • Anorexigenic: Decreases appetite.

  • Key regions involved:

    • Hypothalamus, intestine, liver, brainstem, pancreas.

    • Impact of ablating orexigenic neurons: causes cessation of eating and mortality in rodent models.

Reward Circuit Studies

  • Brain stimulation and behavioral analysis techniques in animal models used to study reward.

  • Olds and Milner (1954) identified reward centers in rodent brains.

  • Specific electrode placements allowed mapping of reward circuitry.

Reward System Characteristics

  • The reward system evaluates rewarding properties of stimuli comprising multiple neural circuits.

  • Major areas involved include:

    • Nucleus Accumbens (NAcc)

    • Lateral Hypothalamus (LH)

    • Ventral Tegmental Area (VTA)

  • Medial forebrain bundle (MFB) enables robust self-stimulation behavior.

Neural Substrates of Hedonic and Motivational Reward

  • Questions on:

    • How to measure 'liking' reactions?

  • Berridge et al. (2020) quantified affective orofacial reactions to assess substance preference.

Endogenous Opioids in Reward Pathways

  • Types include:

    • Enkephalins, dynorphins, endorphins.

  • Opioid receptor subtypes:

    • mu, kappa, delta, are G-protein coupled receptors.

  • Agonists (e.g., morphine) vs. antagonists (e.g., naloxone) impact reward signaling.

Understanding Opioid Pathways

  • Morphine enhances 'liking' responses for palatable foods.

  • Naloxone decreases food intake, particularly with sucrose.

  • Identified 'hedonic hotspots' in the nucleus accumbens crucial for reward processing.

Hedonic Hotspots and Their Connectivity

  • There are additional 'liking' hotspots beyond NAcc.

  • Activation of mu opioid receptors enhances hedonic responses.

  • Hotspots interconnected, contributing to a circuit for pleasure.

Functional Connectivity Assessment

  • Fos plume method to examine functional connectivity among hotspots.

  • Injection with DAMGO and measurement of c-Fos expression as an indicator of neuronal activation.

The Role of Hotspots in 'Liking'

  • Recruitment of hotspots crucial for increased 'liking' responses.

  • Disruption of one hotspot alters overall circuit functioning.

Endocannabinoids in Reward Signaling

  • THCA enhances food intake, particularly of sweet substances.

  • Anandamide targeted injections increase liking expressions for sucrose in NAcc.

  • CB1 and mu receptors co-localized within neurons of NAcc.

Dopaminergic Pathways and 'Wanting'

  • Dopamine identified as a key neurotransmitter in reward system (Olds and Milner).

  • Evidence that dopamine is vital for the motivational aspect ('wanting') of food rewards rather than pleasure itself.

Summary of Key Concepts

  • Dopaminergic pathways generate 'wanting':

    • Anatomically larger than hedonic networks.

    • Can create strong motivation without affecting pleasure.

  • 'Liking' circuits:

    • Composed of interconnected hotspots that can enhance pleasure responses.

Cross-talk between Homeostatic and Reward Circuits

  • Lateral hypothalamic area facilitates communication between homeostatic and reward systems.

  • Orexin as a candidate signaling molecule for this cross-talk, enhancing liking reactions.

Implications for Understanding Eating Disorders

  • Hypothesis: Excessive 'wanting' can surpass 'liking' leading to overeating.

  • Incentive sensitization related to hyperactivity in dopaminergic pathways can trigger food desires.

  • Future research utilizing neuroimaging may enhance understanding of dynamics leading to obesity.