AP Psychology 1.3-1.4: Neural Firing and the Brain

How is the spinal cord protected?

The vertebrae surround and protect the spinal cord, while cerebrospinal fluid cushions it. These protections reduce but do not eliminate the risk of injury.

Spinal cord

A neural relay and processing structure that connects the brain with the peripheral nervous system. It carries sensory information toward the brain, motor commands away from the brain, and can independently coordinate reflexes.

How does the spinal cord connect the brain to the body?

Sensory nerves carry information from the body into the spinal cord and brain, while motor nerves carry commands from the brain and spinal cord to muscles and organs. Spinal nerves branch from the cord at successive vertebral levels.

What are spinal reflexes, and why are they rapid?

A spinal reflex is an automatic response in which sensory input is processed within the spinal cord and immediately produces a motor command. Because the signal does not need to travel to the brain and back, responses such as withdrawing from heat occur quickly.

Examples of spinal reflexes

Withdrawal from a hot object and the knee-jerk response are spinal reflexes. They can occur without conscious input from the brain.

How does the location of a spinal-cord injury affect paralysis?

Damage to a segment can disconnect all segments below it from the brain, producing paralysis below the injury. Injuries lower on the spinal cord generally impair fewer functions than injuries higher on the cord.

Neuroplasticity

The nervous system's ability to change and adapt in response to development, experience, learning, or injury. It can involve forming or eliminating synapses, changing glial cells, reorganizing cortical representations, and sometimes generating new neurons.

How can neuroplasticity contribute to recovery after brain injury?

Undamaged neural circuits may reorganize or strengthen, allowing other regions to support lost functions. Intensive cognitive or speech therapy can promote this adaptation, although plasticity is generally greatest early in life.

Gyri and sulci

Gyri are the raised folds on the cerebral cortex, whereas sulci are the grooves between them. These folds increase cortical surface area and provide landmarks for identifying brain regions.

Longitudinal fissure

The deepest prominent groove in the cerebral cortex, separating the brain into left and right cerebral hemispheres.

Lateralization

The tendency for some functions to be more strongly associated with one cerebral hemisphere than the other. Lateralization is relative rather than absolute because most behaviors depend on interactions between both hemispheres.

How is body control organized across the cerebral hemispheres?

The left hemisphere primarily controls the right side of the body, and the right hemisphere primarily controls the left side. This contralateral organization helps explain deficits after damage to one hemisphere.

Corpus callosum

A large bundle of axons connecting the left and right cerebral hemispheres. It allows information processed in one hemisphere to be shared with the other.

What can split-brain research reveal about hemispheric specialization?

When the corpus callosum is severed, information presented to one hemisphere may not be available to the other. For example, a person may be unable to verbally name an object shown in the left visual field but may be able to draw it with the left hand.

Why does a picture shown in the left visual field create a special problem for a split-brain patient?

The left visual field projects primarily to the right hemisphere, which is generally less specialized for speech production. If the corpus callosum is severed, the information cannot readily reach the verbal left hemisphere.

How do strokes help researchers identify brain functions?

A stroke interrupts blood flow and damages a particular brain region. The resulting behavioral or cognitive deficit can provide evidence linking that region to a specific function.

Forebrain

The largest major division of the brain, containing the cerebral cortex and subcortical structures such as the thalamus, hypothalamus, pituitary gland, and limbic system. It supports complex processes including thought, language, emotion, and memory.

Cerebral cortex

The outer layer of the cerebral hemispheres. It is involved in consciousness, thought, reasoning, language, emotion, memory, and the processing of sensory and motor information.

Frontal lobe

The forward region of each cerebral hemisphere, extending to the central sulcus. It contributes to reasoning, motor control, emotion, judgment, impulse control, and language production.

Motor cortex

A region of the frontal lobe involved in planning and coordinating voluntary movement. It controls movements primarily on the opposite side of the body.

Prefrontal cortex

The frontal-lobe region involved in higher-level cognition, including judgment, reasoning, planning, and impulse control. Damage can produce socially inappropriate or poorly controlled behavior.

Broca's area

A frontal-lobe region essential for producing language. Damage typically causes severe difficulty speaking or forming meaningful language even when speech muscles and comprehension may remain relatively intact.

What contrast distinguishes damage to Broca's area from damage to Wernicke's area?

Broca's-area damage primarily disrupts language production, whereas Wernicke's-area damage primarily disrupts language comprehension. A person with Wernicke's damage may speak fluently but produce or understand language poorly.

Parietal lobe

The lobe behind the frontal lobe that processes information from the body's senses. It contains the somatosensory cortex.

Somatosensory cortex

A parietal-lobe region that processes bodily sensations such as touch, temperature, and pain. Different cortical areas represent different body regions, and body parts with more sensory receptors receive more cortical space.

Why do fingers occupy more somatosensory-cortex area than toes?

Cortical representation reflects sensory receptor density and functional sensitivity rather than physical size. Fingers have many sensory nerves and require precise sensation, so they receive more cortical representation.

Temporal lobe

A lateral cerebral lobe associated with hearing, memory, emotion, and aspects of language. It contains the auditory cortex and Wernicke's area.

Auditory cortex

The primary region for processing auditory information. It is located in the temporal lobe.

Wernicke's area

A temporal-lobe region important for understanding spoken and written language. Damage can leave speech relatively fluent while severely impairing comprehension.

Occipital lobe

The rearmost cerebral lobe, containing the primary visual cortex. It interprets incoming visual information.

Retinotopic organization

The orderly mapping of the visual field onto the visual cortex. Nearby locations in the visual field are represented by nearby locations in the occipital cortex.

Thalamus

A major sensory relay structure that directs information from nearly all senses to appropriate areas of the brain. Smell is the major exception because olfactory information reaches the limbic system more directly.

Limbic system

A group of forebrain structures involved especially in emotion, motivation, and memory. Important components include the hippocampus, amygdala, and hypothalamus.

Hippocampus

A limbic structure essential for learning and the consolidation of new explicit memories. Damage can severely impair the formation of new facts and episodic memories while leaving some skill learning intact.

What did the case of H. M. demonstrate about the hippocampus?

Removing or damaging the hippocampus greatly impaired H. M.'s ability to form new explicit memories. However, he could still acquire some procedural skills, showing that memory systems are functionally distinct.

Amygdala

A limbic structure involved in emotional experience and in assigning emotional significance to memories.

Hypothalamus

A forebrain structure that regulates homeostasis, including body temperature, appetite, and blood pressure. It also links the nervous and endocrine systems and contributes to sexual motivation and behavior.

Midbrain

The brain division located between the forebrain and hindbrain. It includes the reticular formation, substantia nigra, and ventral tegmental area.

Reticular formation

A network extending through the midbrain and into the forebrain and hindbrain that helps regulate arousal, alertness, sleep-wake cycles, and motor activity.

Substantia nigra and ventral tegmental area (VTA)

Midbrain regions containing dopamine-producing cell bodies. They contribute to movement, reward, mood, and addiction; degeneration of these systems is associated with Parkinson's disease.

Hindbrain

The rear brain division containing the medulla, pons, and cerebellum. It includes structures important for vital autonomic functions, communication between brain regions, coordination, and sleep.

Medulla

A brainstem structure that controls essential automatic functions such as breathing, heart rate, and blood pressure.

Pons

A brainstem structure that acts as a bridge connecting the hindbrain with the rest of the brain. It also contributes to regulating brain activity during sleep.

Cerebellum

A hindbrain structure that integrates information from muscles, tendons, joints, and the inner ear to support balance, coordination, movement, and motor skills. It also contributes to procedural memory.

Why could H. M. learn new skills despite severe loss of new explicit memories?

His hippocampal damage disrupted explicit-memory formation, but his cerebellum and other procedural-learning systems remained functional. Thus, skill learning could occur without conscious recollection of the learning episodes.

What is the functional significance of an intact brainstem in a person with severe cortical damage?

The brainstem can maintain vital automatic processes such as breathing and heart rate and can generate some involuntary movements. These functions do not imply intact consciousness, voluntary movement, or higher cognition.

Computed tomography (CT) scan

A brain-imaging method that combines multiple X-ray measurements to construct cross-sectional images. It is useful for detecting structural abnormalities such as tumors or substantial brain atrophy.

Positron emission tomography (PET) scan

A functional imaging method that uses a mildly radioactive tracer to estimate activity in different brain regions, often through changes in blood flow. PET provides relatively limited spatial and temporal detail and exposes the person to radiation.

Why might CT and PET be combined?

CT supplies relatively clear structural information, while PET indicates patterns of brain activity or receptor-related processes. Combining them helps relate functional activity to specific anatomical structures.

Magnetic resonance imaging (MRI)

A structural imaging technique that uses a strong magnetic field and signals from hydrogen atoms to produce detailed images of tissues. It does not require ionizing radiation.

Functional magnetic resonance imaging (fMRI)

A functional form of MRI that tracks changes in blood flow and oxygenation over time to infer activity in brain regions. It provides detailed anatomical images and better temporal information than PET, though it measures blood-oxygen changes indirectly rather than neurons directly.

Electroencephalography (EEG)

A method that records the brain's electrical activity using electrodes placed on the scalp. EEG provides excellent temporal resolution, often within milliseconds, and displays brainwave frequency and amplitude.

Which brain-imaging technique is especially useful for studying the timing of overall brain activity during sleep?

EEG is especially useful because it records electrical activity with millisecond-level temporal accuracy. It provides less precise information about the exact location of the activity.

How do CT, PET, MRI, fMRI, and EEG differ in their primary information?

CT and MRI primarily provide structural information, with CT using X-rays and MRI using magnetic fields. PET and fMRI provide functional information based on tracer distribution or blood-flow and oxygenation changes, while EEG records electrical activity with very high temporal resolution.