Brain Regions and Structures

THE BRAIN: BRAIN REGIONS AND STRUCTURES

Hindbrain, Midbrain, and Forebrain

• Hindbrain:

  • Comprises the medulla, pons, and cerebellum.

  • Directs essential survival functions including breathing, sleeping, and wakefulness.

  • Responsible for coordination and balance.

• Midbrain:

  • Located atop the brainstem.

  • Serves as a connector between the hindbrain and forebrain.

  • Controls certain motor movements and transmits auditory and visual information.

• Forebrain:

  • Contains the cerebral cortex, thalamus, and hypothalamus.

  • Manages complex cognitive activities and sensory and associative functions.

  • Involved in voluntary motor activities.

The Brainstem

• Brainstem:

  • The central core of the brain; begins where the spinal cord enters the skull.

  • Governs automatic survival functions.

• Medulla:

  • The hindbrain structure that forms the base of the brainstem.

  • Controls heartbeat and breathing.

• Pons:

  • Located above the medulla.

  • Aids in movement coordination and manages sleep.

• Crossover Point:

  • The brainstem serves as a crossover point where most nerves from each side of the brain connect with the opposite side of the body.

The Thalamus

• Thalamus:

  • Acts as the sensory control center of the forebrain, positioned atop the brainstem.

  • Directs messages to the sensory receiving areas of the cortex and transmits replies to the cerebellum and medulla.

  • Receives information from all senses, except for smell; routes that information to appropriate brain regions involved in seeing, hearing, tasting, and touching.

  • Functions as a hub facilitating traffic to various destinations.

The Reticular Formation

• Reticular Formation:

  • A nerve network traversing the brainstem into the thalamus.

  • Filters information and plays a crucial role in controlling arousal (state of alertness).

  • Example:

  • Discovered by Magoun in 1949; stimulating a sleeping cat’s reticular formation caused instant alertness, whereas severing it resulted in prolonged coma.

The Cerebellum

• Cerebellum:

  • Known as the “little brain,” situated at the rear of the brainstem.

  • Functions include processing sensory input, coordinating movement output, maintaining balance, and enabling nonverbal learning and memory.

  • Contains approximately half of the brain’s neurons.

  • The processing of most information occurs outside of our conscious awareness.

The Limbic System

• Limbic System:

  • A neural system primarily located in the forebrain, beneath the cerebral hemispheres.

  • Includes the amygdala, hypothalamus, hippocampus, thalamus, and pituitary gland.

  • Associated with emotions and drives.

The Amygdala

• Amygdala:

  • Comprises two almond-shaped neural clusters in the limbic system linked to emotion.

  • Responsible for facilitating aggression and fear responses.

  • Clinical Observations:

  • Individuals with lesions in the amygdala show reduced arousal to stimuli that typically evoke fear or anger.

  • Example: When the amygdala of a cat is electrically stimulated, it prepares to attack, while slight movements can incite fear in response to a mouse.

  • Important to note that fear and aggression involve neural activity across multiple brain regions.

The Hypothalamus

• Hypothalamus:

  • A neural structure within the limbic system, located beneath the thalamus.

  • Directs several maintenance activities such as eating, drinking, and regulating body temperature.

  • Governs the endocrine system and has links to emotion and reward mechanisms.

  • Acts as the brain’s pleasure center or reward center.

  • Example: Engagement with likable people or reading supportive messages activates reward centers in the brain.

  • Some research suggests that disordered behaviors may arise from malfunctions in the brain’s natural systems associated with pleasure and well-being.

  • Individuals genetically predisposed to reward deficiency syndrome may seek substances or behaviors that alleviate negative feelings.

The Hippocampus

• Hippocampus:

  • A neural center located in the limbic system crucial for processing explicit (conscious) memories of facts and events for storage.

  • Damage to the hippocampus from surgery or injury leads to an inability to form new memories related to facts and events.

  • Example: NFL players who experience concussions that lead to loss of consciousness may exhibit a shrunken hippocampus and poor memory retention.

  • The size and function of the hippocampus often decrease with age.

The Cerebral Cortex

• Cerebral Cortex:

  • Considered the ultimate control and information-processing center of the body.

  • Corpus Callosum:

  • A structure connecting the two hemispheres of the brain.

Structures of the Cortex

• Frontal Lobes:

  • Positioned just behind the forehead.

  • Facilitate linguistic processing, muscle movements, higher-order thinking, and executive functions such as planning and judgment.

• Parietal Lobes:

  • Located at the top and to the rear of the head.

  • Receive sensory input relating to touch and body position.

• Occipital Lobes:

  • Situated at the back of the head.

  • Encompass areas responsible for processing information from the visual fields.

• Temporal Lobes:

  • Found roughly above the ears.

  • Include the auditory areas, each receiving information primarily from the opposite ear and aiding in language processing.

Functions of the Cortex

• Motor Cortex:

  • Located at the rear of the frontal lobes, this area is responsible for controlling voluntary movements.

  • Example: Body areas requiring precise control (e.g., fingers and mouth) occupy a larger portion of cortical space.

• Somatosensory Cortex:

  • Located at the front of the parietal lobes; registers and processes touch and movement sensations.

  • Example: Super-sensitive lips are represented in a larger cortical area compared to toes, influencing behaviors like kissing over toe touching.

• Association Areas:

  • Regions of the cerebral cortex not directly involved in primary motor or sensory functions.

  • Engage in higher mental functions including learning, remembering, thinking, and speaking.

Phineas Gage

• Case Study of Phineas Gage:

  • An example of frontal lobe damage impacting personality and impulse control.

  • Gage survived after a rod penetrated his cheek and exited through his skull, damaging his frontal lobes.

  • Initial response: he was able to sit up and speak immediately post-accident.

  • Post-accident changes: friends remarked that he was “no longer Gage,” indicating a behavioral shift to irritability, profanity, and dishonesty.

  • Research shows that individuals with frontal lobe damage exhibit unrestrained moral judgments.

  • Frontal lobes play a key role in guiding individuals toward kindness and away from violence.

  • Damage results in a cognitive awareness of right and wrong but a lack of emotional investment in ethical behavior.

  • Key Insight: Complex mental functions do not reside in isolated areas; psychological health is dependent on the coordinated activity across multiple brain regions.

Tools of Discovery: Neural Measures

• Common Types of Neural Measures:

Sample Findings from Neural Measures

• Symptoms of depression and anxiety correlate with increased activity in the right frontal lobe, associated with behavioral withdrawal and negative emotions.

• Soldiers with PTSD exhibit stronger magnetic fields in the visual cortex compared to those without PTSD when viewing trauma-related images.

• CT scans show that children's brain injuries can predict impairments in intelligence and memory processing.

• Monkeys with an anxious temperament show higher glucose usage in brain areas related to moral judgment and self-control.

• Individuals with histories of violence often have smaller frontal lobes, particularly in regions aiding moral judgment and self-control.

• Long after experiencing a near plane crash, passengers who revisited related material exhibited higher activation in the brain's fear, memory, and visual centers than during exposure to unrelated footage, such as the 9/11 terrorist attacks.