Higher Cortical Functions

Cerebral Cortex

• is “executive suite” of brain

• Site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory, storage, understanding

• Thin (2–4 mm) superficial layer of gray matter

  • Composed of neuron cell bodies, dendrites, glial cells, and blood vessels, but no axons

• 40% of total brain mass

• Conscious behavior involves entire cortex in one way or another

right hemisphere receives info from…

left side of the body (contralateral)

left hemisphere receives info from…

right side of the body (contralateral)

Lateralization

certain functions only occur in only one hemisphere

i.e. speech in left

Cell layer of sensory areas of cortex

• Sensory areas of cortex, such as the primary visual cortex, tend to have a very prominent internal granular cell layer (layer IV),

Cell layer of motor cortex

• have a very meager layer IV but prominent output layers, such as layer V.

3 types of functional areas of cerebral cortex

• Motor areas: control voluntary movement

• Sensory areas: conscious awareness of sensation

• Association areas: integrate diverse information

  • not attached to one cortical function

CT and MRI

• allow for quick identification of

  • tumors

  • intercranial lesions

  • plaque

  • or areas of infarct (dead brain tissue)

PET scans

• localize brain lesions that generate seizures

• based on metabolism

• how much metabolic activity is occurring in each brain region

Radioactive tracer dyes

help visualize specific areas

Functional imaging (fMRI)

• monitor where blood flows in the brain

  • does not monitor electrical signals

• identify parts of brain that contribute to certain functions

• fMRI of brain show specific motor and sensory functions located in discrete cortical areas called domains

• Higher functions are spread over many areas

Brain waves

• are patterns of neuronal electrical activity recorded

• Reflect electrical activity of higher mental functions

• Normal brain functions are continuous and hard to measure

EEG

• Electroencephalogram (EEG) records electrical activity that accompanies brain function

• Electrodes placed on scalp measure electrical potential differences between various cortical areas

Function of EEG

• Used for diagnosing epilepsy and sleep disorders

• Localizes lesions, tumors, infarcts, infections, abscesses

• Used in research and also to determine brain death

What does EEG measure

• EEG measures patterns of neuronal electrical activity generated by synaptic activity in cortex

• Each person’s brain waves are unique

• Patterns change with age, sensory stimuli, brain disease, and chemical state of body

• Measures wave frequency in Hertz (Hz)

  • based on numbers of peaks per second (1 Hz = 1 peak/second)

How are brain waves classified

• Can be grouped into four classes based on Hz:

• Alpha, beta, theta, or delta waves

  • (from most active→ to least active)

Alpha waves

• (8–13 Hz)—regular and rhythmic, low amplitude, synchronous waves indicating an “idling” brain

• occur when someone is awake

Beta waves

• (14–30 Hz)—rhythmic, less regular waves occurring when mentally alert

• occur while awake and need to play close attention to something

Theta waves

(4–7 Hz)—more irregular; common in children and uncommon in awake adults

Delta waves

• (4 Hz or less)—high-amplitude waves of deep sleep and when reticular activating system is suppressed, as during anesthesia; indicates brain damage in awake adult

Language

implementation system involves association cortex of left hemisphere include Broca’s area and Wernicke’s area

Broca’s area

• involved in speech production

• Patients with lesions in Broca’s understand words, but cannot speak

Wernicke’s area

• involved in understanding spoken and written words

• Patients with lesions in Wernicke’s can speak, but words are nonsensible

right hemisphere function

involved with nonverbal language component

Memory

• production of memory + storage and retrieval of information

Different kinds of memory

• Declarative (fact) memory:

  • (names, faces, words, dates, events)

• Nondeclarative memory

  • Procedural (skills) memory:

    • (playing piano)

  • Motor memory:

    • memory of motor skills (riding a bike)

  • Emotional memory:

    • memory of experiences linked to an emotion (heart pounding when you hear rattlesnake)

2 stages of declarative memory storage

• Short-term memory (STM, or working memory): temporary holding of information

  • Limited to seven or eight pieces of information

• Long-term memory (LTM) has limitless capacity

Factors affecting info transfer from STM to LTM

• Emotional state: best if alert, motivated, surprised, or aroused

• Rehearsal: repetition and practice

• Association: connecting new information with old memories

• Automatic memory: subconscious information stored in LTM

Memory consolidation

• involves fitting new facts into categories already stored in cerebral cortex

Parts of brain involved in memory consolidation

• Hippocampus

• temporal cortical areas

• thalamus

• prefrontal cortex

Memory processing

Damage to hippocampus can lead to…

• Damage to hippocampus or surrounding temporal lobe structures on either side results in only slight memory loss

• Bilateral(both sides) destruction causes widespread amnesia

Anterograde amnesia

• consolidated memories are not lost, but new inputs are not associated with old one

• Person lives in the here and now

  • person cannot form NEW memories

• Memory of conversations from just 5 minutes before would not be remembered

Retrograde amnesia

• loss of memories formed in the distant past

• problem with retrieval of memories

What does consciousness involve

• Perception of sensation

  • Voluntary initiation and control of movement

  • Capabilities associated with higher mental processing (memory, logic, judgment, etc.

• Clinically defined on continuum that grades behavior in response to stimuli:

  • Alertness

  • Drowsiness (lethargy)

  • Stupor

  • Coma

Fainting or syncope

• brief loss of consciousness

• Most often due to inadequate cerebral blood flow

• Due to low blood pressure or ischemia from hemorrhage or sudden, severe emotional stress

Coma

• unconsciousness for extended period

• Not the same as deep sleep; oxygen consumption is lowered

Brain death

• irreversible coma

• Ethical and legal issues surround decisions on whether person is dead or alive

Epileptic seizure

• torrent of electrical discharges by groups of brain neurons

  • Prevent any other messages from getting through

• Victim of epilepsy may lose consciousness, fall stiffly, and have uncontrollable jerking

• Epilepsy occurs in 1 of 100 people

  • Epilepsy is not associated with intellectual impairments

  • Genetic factors play a role, but brain injuries, stroke, infections, or tumors can also be causes

Absence seizures

• aka petit mal

• Mild seizures in which expression goes blank for few seconds

• Typically disappear by age 10

• malfunction of Ca2+ channels in thalamus

  • can resolve on its own

Tonic-clonic seizures

• aka grand mal

• Most severe→ last few minutes

• Victim loses consciousness, bones broken during intense convulsions, loss of bowel and bladder control, and severe biting of tongue are common

Aura

• (sensory hallucination)

• may precede seizure

  • constant sensory input triggers the seizures

Control of epilepsy involves…

• anticonvulsive drugs

• Vagus nerve stimulator or deep brain stimulator implantations deliver pulses to vagus nerve or directly to brain to stabilize brain’s electrical activity

Sleep

• state of partial unconsciousness from which person can be aroused by stimulation

• Cortical activity is depressed, but brain stem activity doesn’t change

2 types of sleep

• Non–rapid eye movement (non-REM) sleep

• Rapid eye movement (REM) sleep

Sleep-wake cycle

• During the first 30–45 minutes of the sleep cycle, pass through first two stages (N1 and N2) of non-REM, then move into stage 3 called slow-wave sleep

REM sleep

• EEG, blood pressure, and heart rate decrease

  • About 90 minutes in the REM sleep begins abruptly

• Temporary paralysis, except for rapid eye movements

• Heart rate, respiratory rate, and blood pressure increase; oxygen consumption increases greater than when awake

• Most dreaming occurs in REM

How is sleep regulated by brain

• Alternating cycles of sleep and wakefulness reflect natural circadian (24-hour) rhythm

• Suprachiasmatic nucleus (a biological clock) and preoptic nucleus (a sleep-inducing center) of hypothalamus regulate timing of sleep cycle

• Hypothalamus releases orexins that help cortex to wake up

Why is sleep important

• is the restorative stage

• consolidation of new memories and discarding memories no longer accessed

• During non-REM sleep pulses of cerebrospinal fluid sweep through brain, aiding in washing out of waste products, including some associated with Alzheimer’s disease

• When deprived of sleep, spend more time in REM and slow-wave sleep n next sleep episode attempting to catch up

Narcolepsy

• sleep disorder involving abrupt lapse into sleep from awake state

• Orexins (hypothalmic “wake-up” chemicals) probably destroyed by patient’s immune system; orexin replacement possible treatment

Insonmia

• Chronic inability to obtain amount or quality of sleep needed, possibly caused by depression, anxiety, overuse of caffeine, computer/cell phone use too close to bedtime

  • May be treated by blocking orexin action

Traumatic brain injuries

• include:

  • Concussion: temporary alteration in function

  • Contusion: permanent damage

  • Subdural or subarachnoid hemorrhage: pressure from blood may force brain stem through foramen magnum, resulting in death

  • Cerebral edema: swelling of brain associated with traumatic head injury

Cerebrovascular accidents

• AKA strokes

• Ischemia: tissue deprived of blood supply, leading to death of brain tissue

  • Can be caused by blockage of cerebral artery by blood clot

• Hemiplegia (paralysis on one side of body) sensory and speech deficits may result

• Transient ischemic attacks (TIAs): temporary episodes of reversible cerebral ischemia

  • benign

Alzheimer’s disease (AD)

• Progressive degenerative disease of brain that results in dementia (mental deterioration)

• Memory loss of recent events, shortened attention span, disorientation, eventual language loss, irritability, moodiness, and confusion

What causes Alzheimer’s disease

• Caused by misfolding of proteins that then clump together

• Plaques of beta-amyloid peptides form in brain

• Neurofibrillary tangles inside neurons interfere with transport mechanisms eventually killing neurons

• As brain cells die, functions are lost, and brain shrinks

Treatment of alzheimer’s

• Treatment includes

• drugs to inhibit breakdown of acetylcholine

• block toxic effects of excess glutamate that is released when neurons are damaged, or stimulate destruction of beta-amyloid

Parkinson’s disease

• Degeneration of dopamine-releasing neurons of substantia nigra

• Basal nuclei deprived of dopamine become overactive, resulting in tremors at rest

• Cause unknown, but theories include mitochondrial abnormalities or protein degradation pathways

Treatment of Parkinson’s disease

• Treatment includes L-dopa (dopamine precursor) to alleviate symptoms, deep brain stimulation with electrodes, and implanting stem cells

Huntington’s Disease

• Fatal hereditary motor disorder

• caused by accumulation of protein huntingtin in brain cells

• Leads to degeneration of basal nuclei and cerebral cortex

  • Initial symptoms include wild, “flapping” movements called chorea

  • Later marked by mental deterioration

• Usually fatal within 15 years of onset

  • Treated with drugs that block dopamine effects