2: Brain Regions and Structures

Hindbrain

• The vertebrate brain has three main divisions: hindbrain, midbrain, and forebrain.

• Hindbrain contains structures that direct essential survival functions:

  • Brain stem, which includes the pons and medulla; it is an extension of the spinal cord and sits on top of the spinal cord.

  • At the very top of the brain stem sits the thalamus (attached to the top of the brain stem).

  • The reticular formation passes through the pons and medulla, forming a nerve network that travels through the brainstem into the thalamus and filters information; it is important in controlling arousal.

  • The medulla controls heartbeat and breathing.

  • The pons sits above the medulla and helps control movement and sleep.

  • The brain stem is the central core of the brain beginning where the spinal cord enters; responsible for autonomic, survival functions.

• The thalamus:

  • Directs messages to sensory receiving areas in the cortex.

  • Transmits replies back to the cerebellum and the medulla.

• The picture notes another figure showing the spinal cord, the pons, and the medulla rising into the head region.

• The cerebellum (hindbrain’s little brain):

  • Located at the rear of the brain stem.

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

• The brain processes most information outside of our conscious awareness; we are aware of the results of brain activity (e.g., hearing or seeing) but not of how the brain constructs those auditory or visual experiences.

• The hindbrain’s scope includes the spinal cord relay up to the cerebellum and brainstem regions that control autonomic functions.

• Cognitive summaries:

  • The brain’s sensing and motor systems are distributed; we can influence movement and perception via brain regions that map to body parts, but much processing happens below conscious awareness.

Midbrain

• The midbrain connects the hindbrain with the forebrain.

• It controls some movement and is involved in the transmission of information that enables our senses (such as seeing and hearing).

• It serves as a conduit between lower brain regions and higher cognitive centers, contributing to sensorimotor integration.

Forebrain

• The limbic system (located mostly in the forebrain) is a neural system that is crucial for emotion and drives, and includes:

  • The hypothalamus: lies below the thalamus and directs several maintenance activities; maintains homeostasis (internal state) and regulates hunger, thirst, body temperature, and other bodily processes; it is involved in pleasure rewards and controls the endocrine system by acting on the pituitary gland (master gland).

  • The amygdala (two neural clusters, one on each side): linked to emotion, aggression, fear, and rage; dysfunction in the amygdala has been associated with certain criminal behaviors; when negative events energize the amygdala, such events become more memorable because memories are also stored in the limbic system.

  • The hypothalamus’ role in hormone release is via stimulation of the pituitary gland, triggering hormone release.

  • The hippocampus: a neural center in the limbic system that processes conscious memories for storage; also has neural clusters that influence hunger, thirst, body temperature, and sexual behavior; the hippocampus tends to shrink with age, which is linked to cognitive decline.

• The thalamus is closely connected to the hypothalamus; in the forebrain, the thalamus directs sensory information to the cortex and relays motor and other signals between brain regions.

• The cerebral cortex: the visible outer layer of the brain; a very thin layer of interconnected neurons covering the cerebral hemispheres; acts as the body’s ultimate control and information processing center; it is highly convoluted and appears larger when spread out.

• The cortex is divided into two hemispheres (left and right) with four lobes in each hemisphere: $2$ hemispheres and $4$ lobes.

• The four lobes (from the frontal view):

  • Frontal lobes: located behind the forehead; involved in speaking, muscle movements, planning, and judgments.

  • Parietal lobes: located above the ears and toward the back; involved in processing sensory information.

  • Occipital lobes: located at the back of the head; include areas that receive information from the visual fields.

  • Temporal lobes: located roughly above the ears; include areas that receive information from the ears (auditory processing).

• The cortex functions are studied via electrical stimulation of areas:

  • The motor cortex (rear of the frontal lobes): electrical stimulation can cause movement in specific body parts.

  • The discovery of the motor cortex: Gustav Fritsch and Edouard Hitzig identified it; Jose Delgado demonstrated motor behavior mechanics.

  • Mapping shows a body representation along the cortex (the homunculus); the motor cortex is located in the frontal lobes, in front of the central sulcus (the sulci).

  • The somatosensory cortex (in the parietal lobes, behind the central sulcus) registers and processes body touch and movement sensations; visually parallel to the motor cortex (of note: it is just behind the motor cortex).

• The cortical map reveals that body parts requiring fine motor control or heightened sensitivity occupy more cortical area:

  • The lips, tongue, and fingers have large representations in both motor and somatosensory cortices, reflecting the precision needed for speech and manipulation.

  • The hands and lips have larger representations than for the toes or upper arms; the entire leg is represented much less in comparison.

• Visual and auditory cortices:

  • The visual cortex is in the occipital lobes (rear of the brain) and processes visual information from the eyes.

  • The auditory cortex is in the temporal lobes (above the ears) and processes information from the ears.

• Association areas (in all four lobes):

  • Not primary motor or sensory areas; involved in higher mental functions such as learning, remembering, thinking, and speaking.

  • The prefrontal association areas enable judgment, planning, and processing of new memories.

  • Damage to association areas can produce various losses, explaining the complexity of higher cognitive functions beyond primary sensory/motor processing.

• The “10% brain myth” and critical thinking boxes:

  • Common claim: we only use about 10% of our brain; the box challenges this myth.

  • The myth is debunked by considering evidence from animals and humans with brain damage in association areas, showing that many regions are indeed used for higher-level processing.

  • Even if some areas show little observable response to simple probes, extensive interconnectedness and integration across association areas indicate substantial brain usage beyond the primary areas.

  • The idea that only 10% of the brain is used is inaccurate; brain function is distributed across primary motor, primary sensory, and association areas across all four lobes.

• Throughout the module:

  • There are figures (e.g., Figures 6.5 and 6.7) referenced in the textbook to help visualize brain structures and their functions.

  • The content encourages creating personal notes and diagrams, and working with textbook terminology to solidify understanding.

  • The material connects to broader themes such as brain–behavior links, implications for brain injury (e.g., Phineas Gage) and potential applications (brain–computer interfaces).

• Final guidance:

  • Take time to interact with course content, use Achieve for learning curves, and prepare for practice quizzes and tests.

  • The Zoom sessions will discuss topics like Phineas Gage and brain damage in more detail.

• Ethical, philosophical, and practical implications:

  • The link between amygdala dysfunction and aggression or criminal behavior raises ethical considerations about responsibility and treatment.

  • Understanding brain regions informs debates on free will, responsibility, and treatment of behavioral disorders.

  • Brain–computer interface research (driven by motor cortex mapping) has practical implications for medicine, augmentation, and assistive technologies.

• Notation and conventions:

  • Key numbers: $2$ hemispheres, $4$ lobes per hemisphere, the myth of the $10\%$ brain is discussed and debunked.

  • Terms to review: hindbrain, midbrain, forebrain, brain stem, pons, medulla, cerebellum, thalamus, reticular formation, hypothalamus, pituitary gland, amygdala, hippocampus, cortex, frontal lobe, parietal lobe, occipital lobe, temporal lobe, motor cortex, somatosensory cortex, visual cortex, auditory cortex, association areas, prefrontal cortex.

• Quick recap phrases to memorize:

  • Hindbrain = brain stem + cerebellum + basic life support (breathing, heartbeat, balance).

  • Midbrain = conduit for sensory information and basic movement.

  • Forebrain = limbic system + cerebral cortex; emotion, memory, planning, language, perception.

• Remember to consult Figure 6.5 and Figure 6.7 in your textbook for visual mappings of the brain structures and their cortical representations.