Brain and Behavior
The brain and body work together to regulate thoughts, emotions, and behaviors, with the subcortex playing a crucial role in essential functions like memory, emotion, and movement. Additionally, the endocrine system—a network of glands releasing hormones—affects everything from mood to metabolism, influencing daily actions and long-term development. Understanding these systems provides insight into how biological processes shape behavior. This section explores the core functions of the subcortex and the impact of hormones on human actions, revealing the intricate connections between brain activity and behavior
By the end of this section, you should know about:
- The Subcortex—At the Core of the (Brain) Matter
- The Endocrine System — My Hormones Made Me Do It
Let’s take a closer look at them.
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The Subcortex—At the Core of the (Brain) Matter
The subcortex consists of brain structures located just below the cerebral cortex and controls essential life functions such as hunger, thirst, sleep, and breathing. The subcortex is divided into three main areas: the hindbrain (brainstem), midbrain, and forebrain. Damage to these areas can be life-threatening, as they control fundamental survival functions.
The Hindbrain
The hindbrain is the lower part of the brainstem, where it connects to the spinal cord, and it includes the medulla, pons, and cerebellum.
Medulla: Regulates critical reflexes and life functions, including heart rate, breathing, and swallowing. Damage to the medulla can disrupt these vital functions. Pons: A small bulge on the brainstem that links the medulla with other parts of the brain, such as the cerebellum. It plays a role in sleep and arousal. Cerebellum: Located at the brain’s base, the cerebellum coordinates posture, muscle tone, and body movement. It also aids in memory related to skills and habits. Injury to the cerebellum can impair motor functions like walking, leading to symptoms such as tremors and muscular weakness in diseases like spinocerebellar degeneration.
Reticular Formation (RF)
The reticular formation (RF) is a network within the medulla and brainstem that regulates attention by filtering sensory input to prioritize certain messages over others.
Functions: Influences attention, muscle tone, posture, and controls reflexes related to breathing and other automatic responses. Reticular Activating System (RAS): A part of the RF that keeps the brain alert and responsive to stimuli, such as a sudden noise. It activates the cortex, ensuring that one stays awake and alert, particularly in response to danger.
The Forebrain
The forebrain contains several key structures, including the thalamus, hypothalamus, and the limbic system.
Thalamus: Function: Acts as a sensory relay station, routing signals for vision, hearing, taste, and touch to the cortex. Injury to the thalamus can cause sensory deficits like blindness or deafness.
Hypothalamus: Function: A master control center for emotions and basic drives, including hunger, thirst, and sexual behavior. It integrates information across brain regions to direct many automatic behaviors before they leave the brain.
The Limbic System
The limbic system, which includes the hypothalamus, parts of the thalamus, amygdala, and hippocampus, plays a central role in emotional responses and motivation.
Amygdala: Responsible for fear responses and is critical for processing emotions. It enables quick reactions to danger, helping in survival but can contribute to disorders like phobias or PTSD. Hippocampus: Vital for forming and retaining long-term memories and spatial navigation. It supports memory recall and, when stimulated, can evoke memories and dream-like experiences.
Reward and Aversive Systems
The limbic system includes regions associated with reward (pleasure) and punishment (aversion) pathways: Reward Pathways: Many drugs and pleasurable activities, including listening to thrilling music, activate these pathways, creating feelings of satisfaction. Aversive Areas: When stimulated, these areas cause discomfort, motivating behaviors to avoid negative experiences.
Final Notes on Brain Function and Structure
The brain is an interconnected system where information is processed across multiple areas rather than isolated regions. Human experience, including skills and cultural knowledge, actively shapes brain circuitry, enhancing its complexity and functionality. This feedback loop between experiences and neural development underscores the brain’s adaptability and plasticity.
The Endocrine System — My Hormones Made Me Do It
The endocrine system is a network of glands that releases hormones into the bloodstream, influencing both internal functions and visible behavior. Hormones, like neurotransmitters, are chemical messengers that affect various physical and behavioral processes, including puberty, stress responses, memory, emotions, and even personality.
Major Endocrine Glands and Hormone Functions
Pituitary Gland (“Master Gland”)
Location & Role: A small gland at the brain’s base that regulates growth and influences other glands.
Growth Hormone: Essential for body development. Low production causes hypopituitary dwarfism (small stature with normal proportions), while high production leads to gigantism and, in adulthood, acromegaly (enlarged facial and limb bones).
Oxytocin: Promotes bonding, trust, stress reduction, and plays a key role in childbirth, parenting, and social behavior.
Connection to the Hypothalamus: The pituitary gland is regulated by the hypothalamus, creating a link between brain activity and hormonal responses.
Pineal Gland
Function: Produces melatonin in response to light, regulating sleep cycles. Melatonin levels rise in the evening, peak around midnight, and drop by morning, signaling bedtime.
Thyroid Gland
Location: Found in the neck. Hormonal Influence on Metabolism: Regulates energy use in the body, impacting metabolism. Hyperthyroidism: Overactive thyroid results in weight loss, nervousness, and tension. Hypothyroidism: Underactive thyroid can lead to fatigue, obesity, sluggishness, and sometimes depression.
Adrenal Glands
Location: Positioned atop the kidneys. Hormones: Includes epinephrine (adrenaline) and norepinephrine, which prepare the body for “fight or flight” responses. Epinephrine: Linked with fear; it raises heart rate, releases energy, and prepares the body for action. Norepinephrine: Associated with anger; it increases alertness and blood flow to muscles. Corticoids: Regulate salt balance, assist in managing stress, and provide a secondary source of sex hormones. Effects of Oversecretion: Can cause exaggerated male characteristics (virilism) or premature puberty.
Sex Hormones
Testosterone (Androgens): Prominent in both sexes, produced mainly by testes in males and in smaller quantities by the adrenal glands in both sexes. Anabolic Steroids: Synthetic versions of testosterone used to enhance muscle growth, sometimes causing severe side effects such as aggression, heart issues, liver damage, and stunted growth in adolescents.
Brain and Behavior: Hormones and Their Behavioral Effects
Hormones play a significant role in:
Stress Response: The adrenal glands release hormones in stressful situations, preparing the body for physical action. Sex Drive: Androgens, including testosterone, affect libido in both males and females. Memory Formation: Emotional experiences trigger hormones that help to reinforce memories. Personality and Emotions: Hormonal imbalances can impact personality traits, mood, and responses to stimuli (e.g., anger vs. fear).
Studies have shown that hormone levels can be influenced by external factors, such as: Watching movies with different emotional content (e.g., romantic scenes increasing relaxation-linked hormones). Environmental and situational stimuli affecting hormone release and thus behavior and mood.
Brain and Behavior: Left- and Right-Handedness: Differences and Insights
Introduction to Handedness: Handedness refers to the preference for using one hand over the other. Historically, left-handed individuals have faced negative stereotypes, with terms like “sinister” (meaning left in Latin) often used to describe them. Right-handed people, in contrast, have been praised for traits like dexterity and skill.
This section explores the causes, differences, and implications of handedness, focusing on the connection between handedness and brain functioning.
Assessing Handedness
Right vs. Left Hand Dominance: The common way to assess handedness is to write your name with both hands. Most people find writing easier and more controlled with their dominant hand. The dominance of one hand is a reflection of superior motor control in one hemisphere of the brain, typically the left hemisphere for right-handed individuals and vice versa for left-handed individuals.
Handedness as a Spectrum: Handedness isn’t always binary. Most people are strongly right- or left-handed, but some are ambidextrous or show inconsistencies in hand preference.
Other Sidedness: Handedness is just one form of sidedness. People also show preferences for their dominant foot, eye, ear, and even nostril. Handedness remains the most significant indicator of this trait.
Brain Dominance and Language Processing
Brain Hemispheres and Handedness: The left hemisphere of the brain controls the right hand and is typically responsible for language processing. While 95% of right-handed individuals have language centers in the left hemisphere, around 70% of left-handed individuals do the same. However, 19% of left-handers and 3% of right-handers process language in the right hemisphere. Some left-handed individuals use both hemispheres for language.
Indicators of Brain Dominance: Handwriting style and hand gestures provide clues about brain dominance. Right-handers who write with a straight hand tend to have left-brain dominance, while left-handers with hooked hand-writing often have right-brain dominance.
Causes of Handedness
Genetics and Environmental Influence: Handedness is partly inherited. Prenatal preferences for hand use can persist after birth, suggesting that parents should not force a child to use a particular hand. Studies show that left-handedness is more common in males and may be influenced by a gene on the X chromosome.
Environmental Factors: Social pressures, birth conditions (e.g., premature birth), and cultural influences also contribute to handedness. For instance, left-handedness is less common in collectivist societies like Japan and India due to social stigmas, compared to individualist cultures like the U.S.
Brain and Behavior: Advantages and Disadvantages of Left-Handedness
Disadvantages:
Health Issues: A small minority of left-handed individuals may have higher rates of learning disorders or immune-related diseases due to birth complications or inconsistent handedness. Accident-Prone: Left-handed people may have higher accident rates because most tools and environments are designed for right-handed people, making it harder for them to use everyday objects effectively.
Advantages:
Creativity and Visual Skills: Left-handed individuals tend to excel in fields requiring visual or spatial skills. Historically, many renowned artists (e.g., Leonardo da Vinci, Pablo Picasso) were left-handed, possibly due to better use of the right hemisphere for visual imagery. Sports: Left-handed athletes may have an advantage in certain sports like tennis, boxing, and fencing, where their opponents are more accustomed to right-handed players. Brain Symmetry: Left-handed individuals often exhibit less lateralization in their brains, meaning their left and right hemispheres are more alike in size and function. This symmetry can provide advantages in memory and cognitive flexibility. Cognitive and Musical Benefits: Left-handers, particularly those who are moderately left-handed or ambidextrous, show better-than-average memory skills (e.g., pitch memory). Additionally, left-handed or ambidextrous individuals are often more skilled in math and music. Recovery from Brain Injury: Left-handed individuals tend to recover more easily from brain injuries, as their less lateralized brains allow them to rely on both hemispheres for language and cognitive functions.