Source: General Psychology, The Ohio State University, Chapter 6
Tags: sleep stages, REM, EEG, emotions, drives, homeostasis, hypothalamus, hunger, lateral hypothalamus, ventromedial hypothalamus, sex drive, testosterone, amygdala, reward system, dopamine, VTA, nucleus accumbens, addiction, dependence, split-brain, corpus callosum
Difficulty: Intermediate | Prerequisites: Chapter 5 notes (neurotransmitters, autonomic nervous system, brain structures)
This chapter pulls together several threads: the stages of sleep and how they are measured, the distinction between emotions and drives, the hypothalamus's role in hunger and sex drive, the amygdala's role in emotion, the brain's reward system and its relationship to addiction, and the split-brain procedure. It is the heaviest chapter on the exam in terms of sheer volume of distinct topics, so give yourself time. The neurotransmitter concepts from Chapter 5 (especially dopamine and ACh) come up repeatedly here.
Sleep moves through measurable stages (from light NREM through deep slow-wave sleep to REM), and the balance shifts across the lifespan. Emotions are goal-specific motivation states; drives are benefit-specific and tied to homeostasis. The hypothalamus controls hunger through its lateral and ventromedial areas. Sex drive depends on testosterone in males (mediated by the medial preoptic area) and is more complex in females. The amygdala regulates fear, aggression, and emotional memory. The brain's reward pathway (VTA, nucleus accumbens, prefrontal cortex) runs on dopamine and is hijacked by addictive drugs. The split-brain procedure shows that the two hemispheres specialise in different cognitive functions.
Electroencephalogram (EEG)
A recording of brain wave activity from electrodes on the scalp surface. The primary tool for measuring sleep stages.
Electrooculogram (EOG)
A recording of eye movements. Used alongside EEG to identify REM sleep.
Electromyogram (EMG)
A recording of muscle tone. Drops to its lowest during REM sleep.
Slow-wave sleep (SWS)
The deeper stages of NREM sleep characterised by delta waves. Divided into stages with 20–50% delta activity and stages with more than 50% delta activity.
REM sleep
Rapid eye movement sleep. Brain activity resembles waking (emergent Stage 1 pattern), but muscle tone is at its lowest. Associated with dreaming.
Emotion
A goal-specific motivational state. Emotions (love, hate, fear) are set by beliefs about the value of a goal.
Drive
A benefit-specific motivational state produced by hormones released by the brain in response to the need for a beneficial goal. In simple terms, drives push you toward things your body needs (food, water, warmth).
Homeostasis
The tendency to maintain some physiological variable within a fixed range, called a set point. Think of it as the body's thermostat: when a variable drifts too far from the target, a drive kicks in to correct it.
Regulatory drive
A drive that is nearly homeostatic, maintaining a set point but also anticipating future needs rather than only reacting to current ones (e.g., hunger, thirst).
Non-regulatory drive
A drive that helps preserve an animal's fitness but has no set point and no direct feedback about how well the organism's needs are being met (e.g., sex drive).
Lateral hypothalamus (LH)
The region of the hypothalamus that monitors energy stores, controls metabolic reflexes, codes food incentives, and processes taste and pleasure of food. Lesions cause aphagia (failure to eat); stimulation causes weight gain.
Ventromedial hypothalamus (VMH)
The region of the hypothalamus that controls metabolic functions such as insulin secretion and affects the palatability of food. Lesions cause hyperphagia (overeating) and obesity; stimulation causes aphagia.
Aphagia
Failure to eat. Produced by lateral hypothalamus lesions or ventromedial hypothalamus stimulation.
Hyperphagia
Compulsive overeating. Produced by ventromedial hypothalamus lesions.
Medial preoptic area
A region of the hypothalamus critical for male sex drive. Tiny amounts of testosterone placed here restore sex drive in castrated animals; the same amount placed elsewhere has no effect.
Coolidge effect
The phenomenon in which a male animal that has become sexually exhausted with familiar partners will resume mating when a novel female is introduced. Attributed to an increase in dopamine in the limbic system.
Estrous cycle
The reproductive cycle in most female mammals (except humans and musk shrews) that controls ovulation and sexual receptivity.
Menstrual cycle
The reproductive cycle in human females that controls ovulation. Unlike the estrous cycle, human females can experience sex drive at any point in the cycle.
Amygdala
A brain structure involved in regulating emotion. Bilateral removal reduces fear and aggression and impairs the ability to interpret emotions in others.
Ventral tegmental area (VTA)
A brain region whose dopamine-containing neurons project to the nucleus accumbens and prefrontal cortex, forming the core of the reward pathway.
Nucleus accumbens
A structure in the reward pathway where dopamine is released in response to rewarding stimuli. Electrical stimulation here is positively reinforcing; rats will press a lever repeatedly to receive it.
Addiction
Compulsive use of a substance, mediated by the reward pathway (VTA, nucleus accumbens, prefrontal cortex).
Dependence
A physiological state in which stopping a drug produces a withdrawal syndrome. Mediated by the thalamus and brainstem. A person can be dependent without being addicted.
Corpus callosum
The large bundle of nerve fibres connecting the left and right hemispheres of the brain. Severing it (the split-brain procedure) prevents information from transferring between hemispheres.
How sleep is measured
EEG: brain wave patterns from the scalp
EOG: eye movements
EMG: muscle tone
The stages
Initial sleep onset: alpha and theta waves
Stage 2: K complexes and sleep spindles
Slow-wave sleep (lighter): 20–50% delta waves
Slow-wave sleep (deeper): more than 50% delta waves
REM sleep: brain activity returns to a pattern resembling Stage 1 (emergent Stage 1); eyes move rapidly; muscle tone is at its lowest
Changes across the lifespan
As you age, time spent awake increases and time in REM sleep decreases
Infants spend the most time in REM; elderly adults spend the most time awake during the night
Functions of sleep
Restoration: growth hormone release, tissue repair
Adaptive: energy conservation, predator avoidance (sleeping during vulnerable hours)
Cognitive: learning consolidation, unlearning irrelevant information, neural reorganisation
Emotions
Goal-specific motivational states
Examples: love, hate, fear, joy
Set by beliefs about the value of a goal
The emotion you feel depends on what you want and how you evaluate your progress toward it
Drives
Benefit-specific motivational states
Produced by hormones released by the brain in response to a biological need
Help preserve homeostasis by maintaining variables near a set point
Regulatory drives
Nearly homeostatic: they maintain a set point but also anticipate future needs
Examples: hunger, thirst
Non-regulatory drives
Help preserve fitness but have no set point
No direct feedback mechanism to tell the organism how well its needs are being met
Example: sex drive
Lateral hypothalamus (LH)
Monitors energy stores (via the liver)
Controls use of energy stores (metabolic reflexes)
Codes food incentives
Processes taste and pleasure of food
Lesions to the LH destroy all of these functions, causing aphagia
Stimulation of the LH causes weight gain
Ventromedial hypothalamus (VMH)
Controls metabolic functions such as regulating insulin secretion
Affects palatability of food, making tastiness the most important factor in feeding
Lesions produce hyperphagia and obesity
Stimulation causes aphagia
Additional points
Weight is heritable
Healthy weight control is not the same as general self-control (it involves specific hypothalamic regulation, not willpower alone)
Male sex drive
Maintained by testosterone
Castration (removing the testes, the main source of testosterone) causes a severe decline in sex drive
Injecting testosterone in castrated animals fully restores sex drive
Placing a tiny amount of testosterone into the medial preoptic area of the hypothalamus restores sex drive in castrated animals; the same amount elsewhere has no effect
Small lesions in the medial preoptic area abolish sexual behaviour in male rats
In human males: castrated men experience a decline (though not complete loss) of sex drive, which testosterone injections restore. Some men with naturally low testosterone still function sexually, but testosterone injections sharply increase their sexual behaviour in double-blind studies. Normal variation in testosterone within the typical range does not appear to strongly affect sex drive.
The Coolidge effect
A sexually exhausted male animal will resume mating when a novel female is introduced
Observed in rats, farm animals, and possibly primates
Attributed to an increase in dopamine levels and the effect on the limbic system
Female sex drive
Males can always pass on their genes; females can only do so when ovulating
In most mammals (except musk shrews), ovulation is controlled by the estrous cycle
In humans, ovulation is controlled by the menstrual cycle
Human females can experience high or low sex drive at any point in the cycle, but hormones still influence sex drive
Three sources of evidence that the amygdala plays an important role in regulating emotion:
Bilateral removal of the amygdala causes reduction of fear and aggression, impaired ability to interpret emotions in others, and may be linked to autism
Stimulation of the amygdala produces aggressive behaviour
The size and structure of the amygdala differs between men and women, which could explain why women tend to have stronger memories for emotional events than men
The reward pathway
Core structures: ventral tegmental area (VTA), nucleus accumbens, prefrontal cortex
VTA neurons contain dopamine, which is released in the nucleus accumbens and prefrontal cortex when the pathway is activated by a rewarding stimulus
Natural rewards (food, sex) stimulate dopamine neurotransmission through this pathway
This mechanism of controlled dopamine release and reuptake has been shaped by evolution to reward survival-critical activities
Discovery through animal research
Rats were trained to press a lever for a small electrical jolt to the nucleus accumbens. They pressed it repeatedly because it was pleasurable (positive reinforcement)
When the electrode was placed in a nearby area not connected to the nucleus accumbens, the rat did not press the lever
If dopamine release was blocked (by a drug or by destroying the pathway), the rat stopped pressing
Rats also self-administer heroin through a needle placed directly into the nucleus accumbens, pressing a bar repeatedly to receive it. If the needle is placed in a nearby area, the rat will not self-administer
How drugs hijack the system
Addictive drugs produce much larger dopamine surges than natural rewards
Over time, enzymes build up that remove dopamine more efficiently, which is why tolerance develops and more of the drug is needed
The frontal lobe (executive function) is affected, impairing decision-making
Addiction vs. dependence
Addiction: compulsive use, driven by the reward pathway (VTA, nucleus accumbens, prefrontal cortex)
Dependence: a physiological state where stopping the drug causes withdrawal symptoms, driven by the thalamus and brainstem
It is possible to be dependent without being addicted. Patients treated with morphine for cancer pain may become dependent (they get withdrawal symptoms if the drug is stopped) but are not compulsive users and are not addicted
Hospital patients given morphine for post-surgical pain are unlikely to become addicted: the use is short-lived and the analgesic/sedating effects predominate over euphoria
Hemispheric specialisation
Left hemisphere: language, maths, logic, analytical processing
Right hemisphere: intuition, creativity, art, music, spatial perception, face recognition
What the split-brain procedure reveals
The corpus callosum is cut, preventing information from transferring between hemispheres
Split-brain patients can only identify information verbally when it is presented in the right visual field (processed by the left hemisphere, which controls language)
If a spoon is flashed in the left visual field (processed by the right hemisphere), a split-brain patient cannot say it was a spoon
But if the patient is blindfolded and asked to find the object with the left hand (controlled by the right hemisphere), they can do so
This demonstrates that each hemisphere processes information independently when the corpus callosum is severed, and that the left hemisphere has a near-monopoly on verbal report
"REM sleep is the deepest stage of sleep." REM is actually characterised by brain activity that resembles waking. The deepest sleep is slow-wave sleep (more than 50% delta waves).
"Emotions and drives are the same thing." Emotions are goal-specific (tied to beliefs about a goal's value); drives are benefit-specific (tied to biological needs and homeostasis). They overlap but are distinct categories.
"The lateral hypothalamus is the hunger centre and the ventromedial hypothalamus is the satiety centre." This is an oversimplification. Both areas play roles in regulating energy stores, metabolic function, and food palatability. The relationship is more nuanced than a simple on/off switch.
"Addiction and dependence are the same." They are mediated by different brain regions. Dependence (withdrawal when the drug stops) is possible without addiction (compulsive use driven by the reward pathway).
⚠️ Know all five sleep stages, the three physiological measures (EEG, EOG, EMG), and how sleep changes across the lifespan.
⚠️ Be able to distinguish emotions (goal-specific) from drives (benefit-specific) and give two examples of each.
⚠️ Know the effects of lesions vs. stimulation for both the lateral and ventromedial hypothalamus. This is a classic exam question with lots of potential for mix-ups.
⚠️ Understand the male sex drive's dependence on testosterone and the medial preoptic area. Be ready to discuss the Coolidge effect and its dopamine basis.
⚠️ Know three sources of evidence for the amygdala's role in emotion.
⚠️ Be able to describe the reward pathway (VTA, nucleus accumbens, prefrontal cortex), explain how dopamine mediates reward, and distinguish addiction from dependence.
⚠️ Know what the split-brain procedure is and what it reveals about hemispheric specialisation. The spoon-in-the-left-visual-field example is a staple.
True or False: REM sleep features the highest proportion of delta waves.
Fill in the blank: Lesions to the lateral hypothalamus cause __________ (failure to eat).
True or False: A person can be dependent on morphine without being addicted to it.
Fill in the blank: The __________ connects the two hemispheres and is severed in the split-brain procedure.
True or False: The Coolidge effect is attributed to a surge in serotonin.
Answers: 1. False (SWS has the most delta waves; REM resembles waking). 2. Aphagia. 3. True. 4. Corpus callosum. 5. False (it is attributed to dopamine).
Q: What are the stages of sleep, how are they measured, and how do they change over the lifespan?
A: Sleep is measured by EEG (brain waves), EOG (eye movements), and EMG (muscle tone). Stages progress from initial alpha/theta waves, through Stage 2 (K complexes, sleep spindles), to slow-wave sleep (20–50% then more than 50% delta), and finally REM (brain activity resembles Stage 1, rapid eye movements, minimal muscle tone). Over the lifespan, waking time increases and REM sleep decreases.
Q: What are the differences between emotions and drives? Give two examples of each.
A: Emotions are goal-specific motivational states set by beliefs about a goal's value (examples: love, hate). Drives are benefit-specific motivational states produced by hormones in response to a biological need (examples: hunger, thirst). Drives help preserve homeostasis; emotions do not necessarily have a set point.
Q: How does the hypothalamus control hunger and eating behaviour?
A: The lateral hypothalamus monitors energy stores, controls metabolic reflexes, codes food incentives, and processes taste/pleasure. LH lesions cause aphagia; stimulation causes weight gain. The ventromedial hypothalamus controls insulin secretion and food palatability. VMH lesions cause hyperphagia and obesity; stimulation causes aphagia.
Q: Describe three sources of evidence that the amygdala regulates emotion.
A: (1) Bilateral removal reduces fear and aggression and impairs the ability to read emotions in others. (2) Stimulation produces aggressive behaviour. (3) Structural differences between male and female amygdalae may explain why women tend to have stronger emotional memories.
Q: What is the brain's reward system and how does it relate to drug addiction?
A: The reward pathway runs from the VTA through the nucleus accumbens to the prefrontal cortex, using dopamine. Natural rewards activate this pathway at calibrated levels. Addictive drugs produce much larger dopamine surges, leading to tolerance (more drug needed) and compulsive use. Addiction (compulsive use, reward pathway) differs from dependence (withdrawal symptoms, thalamus/brainstem). One can be dependent without being addicted.
Q: What is the split-brain procedure and what does it reveal about cognitive organisation?
A: The corpus callosum is severed, preventing information transfer between hemispheres. The left hemisphere specialises in language, maths, and logic; the right in spatial perception, creativity, and face recognition. A split-brain patient cannot verbally name an object flashed in the left visual field (right hemisphere) but can identify it by touch with the left hand (also right hemisphere). This shows each hemisphere has distinct, specialised functions.
Sleep connects to the adaptive/evolutionary framework from Chapter 3 (predator avoidance, energy conservation). The dopamine-based reward system ties directly back to Chapter 5's agonist/antagonist concepts (cocaine as a dopamine agonist, anti-psychotics as dopamine antagonists). The hypothalamic control of hunger and sex drive builds on the autonomic and endocrine system material from Chapter 5. The split-brain findings connect to broader questions about consciousness that run all the way back to Wundt and the structuralists in Chapter 1.
sleep stages NREM REM, EEG brain waves, EOG eye movements, EMG muscle tone, alpha theta delta waves, K complex sleep spindle, slow-wave sleep SWS, REM rapid eye movement, sleep functions restoration cognitive, emotions vs drives, goal-specific benefit-specific, homeostasis set point, regulatory drive, non-regulatory drive, lateral hypothalamus LH, ventromedial hypothalamus VMH, aphagia hyperphagia, hunger regulation, testosterone sex drive, medial preoptic area, Coolidge effect dopamine, estrous cycle menstrual cycle, amygdala emotion fear aggression, reward pathway VTA nucleus accumbens, prefrontal cortex dopamine, addiction vs dependence, morphine tolerance withdrawal, split-brain procedure, corpus callosum, hemispheric specialisation, left brain right brain, visual field processing