Cognitive+Neuroscience

Copyright © Allyn & Bacon 2005

(Cognitive) Neuroscience


21st Century =Cognitive Neuroscience

Late 1970s =Cognitive psychology + neuroscience “The study of the relationships between neuroscience and cognitive psychology Study the brain, learn about the mind

New ways to study Cognitive Psychology Human brain – Next frontier The brain is small but vast and complicated Basic brain geography already known Now map out specific regions and functions and relate

them to cognitive processes


Cognitive Neuroscience These two disciplines help each other: Cognitive psychologists can find physical evidence for

their theoretical structures of the mind. Neuroscientists can relate their findings to

comprehensive models of cognition. Correlate brain pathology and behavior. Build models of the mind that include neurological functions. Simulate human cognition with computer models of neurological

functioning. Imaging techniques reveal structure and process.


Development of Neuroscience

Early 19th (cont.) Mid Late 1920

Medical investigations improvements in neurons & glia modernof injured soldiers leads microscopes discovered view to “lesion approach”

“Geological Analogy”Franz Joseph Gall Augustus von Waller Gamillo Golgidevelops the pseudo- discovered chemical Santiago y CajalScience of phrenology way of staining nerves & brain composition


Development of Neuroscience Late 1800s-1900s= as the scientific study of psychology grows,

so too does the scientific study of the brain and nervous system

Medical investigations of injured soldiers connected behavioral problems with damaged parts of brain this “lesion approach” was applied to animals - cause damage and

study behavioral consequences As geologists studied the layers of the Earth, neuroscientists

studied the layers of the brain the deeper layers thought to be more primitive the upper layers thought to be more for complex thought and newer

evolutionarily Phrenology (Franz Joseph Gall)

pseudoscience which studied the bumps on the skull to assess personality (was empirically wrong)

different characteristics were localized in different places in brain (important-- led to animal/people stimulation of different brain areas)


Development of Neuroscience With advances in staining and microscopic methods discovered two

main classes of brain cells: Neurons- nerve cells of the brain neuroglia (or glia)– cells that act as “glue” holding it all together

Important theories of brain make-up developed Camillo Golgi:

brain is composed of large multinucleated cells forming a complex net (syncytium) Santiago Ramón y Cajal

brain is composed of nerve cells linked together by long extensions Cajal was right!

Modern chemical transmission and biological electricity theory originated with the work of Sir Henry Dale & Otto Loewi: Muscles activated and heartbeat and other pertinent organs regulated by chemical

signals arising in the nerves And that bio-electricity is an essential process in the spread of excitability within cells–

activating chemical messages when it reaches the junction between neurons


Mind-Body Issues Physical versus mental world

Body Operates in the physical world Includes physical objects (including brain) and laws that govern them

Mind Operates in the psychological World Comprises the processes carried out by the brain-- includes cognition (thinking,

memory, perceiving, judging, emotions, creativity, etc.)and the laws (often harder to detect) that govern them

Historically, “behavior” was what was only publicly observable (behaviorism) Historically, “mind” was something different from the brain - was more

abstract - possibly even a “soul” -- dualistic belief With technological advances, brain activity is now publicly observable

behavior

Dichotomy (split) of mind-body dualists Only real world is the mind and the physical world is an illusion Only real world is the physical world and the mind is ultimately only a function of

the brain


Mind-Body Issues

Contemporary view: Everything psychological is simultaneously

neurological All cognition is the result of neurological activity

(the mind is what the brain does - the mind is a result of the overall activity of the brain)

Based on cognition, all behavior is predicated on neural activity


Central Nervous System

Central Nervous System (CNS): All parts of nervous system that lie within the bones of the skull & spine Brain = a complex organ specialized to carry out

major acts of living Centerpiece of the CNS

Spinal Cord = long tubular column of neural tissue surrounded by a ring of bone running from base of skull to lower back “Information Superhighway”


Cells of the Nervous System

2 Main types of cells make up the Nervous System:

Neurons Neural Networks = Clusters of interconnected

neurons that form & strengthen from experience

Glial cells (Glia or Neuroglia) Means “Glue” Provide structural support, nutrients,

insulation & help with waste removal


Neurons Neurons work in circuits linked together

convergently divergently

linking sites are called synapses

chemical neurotransmitters carry messages across synaptic gap - called synaptic transmission


Characteristics Unique to Neurons Dendrite - protrude from cell body (soma)

- receives information from other neurons Soma manufacture proteins, axons store

them in synaptic vesicles - microtubules provide transportation for the proteins and other substances

Axon - main “protruding element” - sends information to other neurons - sometimes branching widely (called collateral axons) or looping back to near original axon (called recurrent collaterals)

Axon Terminals: branched, knob-like tips at the end of an axon (buttons)

Myelin sheaths- shinny white layer of fatty cells on the axon that provides insulation and helps speed electrical impulses


The Neuron at Rest Inside of the neuron is Negatively polarized - has a negative

electrical potential relative to outside of plasma membrane (resting potential)

caused by the differential concentration on negatively charged proteins in cell

So there is strong force pulling positively charged ions into cell -but can’t get in because of semi-permeability (selective access) of the plasma membrane so negative charge maintained

membrane has selective channels (openings) which are usually closed and will only open when get signal to do so - “gated” for specific substance

channels for potassium, sodium, etc.


The Nerve Impulse Neuron becomes slightly positive from receiving

certain chemicals at synapse Due to this slight change in potential, sodium (and

sometimes calcium) gates open allowing those ions to rush in

Inside of axon becomes positively charged briefly, causing the next set of channels to open, etc. (called action potential or depolarization)

The nerve impulse thus moves along the length of the axon


The Nerve Impulse

Action potential lasts 1/1000 of a second Is a simultaneous outflow of potassium ions and

closing of sodium and calcium channels ion pumps continuously pump out sodium


The Nerve Impulse


How Neurons Communicate

Through synaptic neurotransmitters (chemical messengers) which flow across synapse

Presynaptic neuron - sending neuron Postsynaptic neuron - receiving neuron neurotransmitters released from synaptic vesicles by

presynaptic neuron neurotransmitters fit into receptor sites on postsynaptic neuron

like a key in a lock to open ‘gated” channels Excess neurotransmitter removed through enzymatic

degradation (killer enzymes released from postsynaptic neuron) or reuptake (re-absorption and re-packaging of presynaptic neuron)


How Neurons Communicate Autoreceptors on presynaptic neuron monitor and

help regulate amount of neurotransmitter in synapse Generally two types of synaptic messages

Excitatory Inhibitory

Postsynaptic neuron fires when reaches a neural threshold potential - determined by amount of neurotransmitter released

impulses can sum across time (1 fires many times) and space (many diff. axons at once)


Glia Glia

astrocyte clean up excess

neurotransmitter provide support &

nutrients oligodendrocyte

provides cellular insulation (myelin) which increases speed of impulse

called Schwann cell in PNS


Organization of the Brain Phrenology

Bumps = Character, personality, etc. Pseudoscience Produced the concept of Localization

A function (motor activity, language processing, sensing, etc. are each associated with a specific brain area)

Flourens’ Aggregate Field Theory Major sensory and motor functions not a matter of localizations in specific

regions but also distributed in other parts of the brain (holistic view– cognitive processes distributed throughout)

Compromise View (current) some processes localized to specific regions or group of close regions in the

brain (motor responses, sensory terminals, vision and some language processing)

Higher-order cognitive functions such as memory, perception, thinking and problem solving are divided into sub-functions distributed throughout the brain

ANATOMICAL ORGANIZATION OF THE BRAIN IS LARGELY HIERARCHICALOPERATIONAL ORGANIZATION IS OFTEN NOT HIERARCHICAL

~widely spread brain parts may form “alliances” to carry out specific functions.


Anatomy of the Brain

Major sensory relay

Internal regulation

Master glad endocrine system

Regulates fear/aggression

Important for memory formation

Important for movement

Relay- cortex & cerebellum

Regulates heartbeat/breathingRelay- sleep/arousal


Anatomy of the Brain: CortexCerebral Cortex: brain’s most outermost layer Most recent evolutionarily Credited with “highest” intellectual functions: thinking, planning,

problem solving ¼ inch thick, densely packed neurons Ridges (gyri) and grooves (sulci) with deep and prominent sulci

(fissures) provides large surface area

Cortex is divided into 4 sections

(lobes) based on location:•Frontal lobe (motor and executive functions)•Temporal lobe (audition, speech, emotion) •Parietal Lobe (sensory)•Occipital Lobe (vision)


Cortex: Areas of Localization

Localization:

Motor Cortex:Sends impulses to voluntary musclesLocated in back Frontal Lobe

Somatosensory Cortex:

Receives sensory information Located in front Parietal lobe


Cortex: Areas of Localization

Localization:

Visual Cortex: primary processing area for vision

Auditory Cortex: primary processing are for hearing


Cortex: Areas of LocalizationLocalization:

Broca’s area: directs the muscle movements in speech production; damage to which results in Broca’s aphasia (difficulties producing sounds of speech)

Wernicke’s Area: involved in the comprehension of language; damage to which results in Wernicke’s aphasia (difficulties comprehending language - speech appears quite normal

Arcuate Fasciculus:connects Wernicke’s and Broca’s areas


Processing of the Cortex

Yet for actual language processing, the brain operates as an integrated system!


Cortex: Association Areas

Distributed in the tradition of Flourens: Large areas of

“uncommitted” cortex in each lobe of cerebral cortex integrates information

from many parts of brain highly interconnected

with one another Account for about 75%

of the cortex


Cortex: Association Areas

Parietal lobe association cortex integrates somatosensory

information with sight & sound

Limbic association cortex emotional tone and memory

Prefrontal lobe association cortex working memory, planning, use

of cognitive strategies, cognitive flexibility, decision-making

develops slowly across time

frontal, temporal & occipital lobes work together to produce language in humans


Cortex: Local vs. Distributed Lashley’s theory of Mass Action:

Learning is not tied to specific neurons Memories are distributed throughout the Cortex Brain operated holistically rather than compartmentally

Contemporary View: Many mental functions seem localized but further processing

seems to take place in different sites Many higher-order mental functions (thinking, learning, memory)

involve several cortex areas– neural processing is redundant– distributed throughout the brain and processing in parallel at many locations

Damage to the brain does not always lead to reduction of cognitive performance (redundancy and plasticity)


Cortex: Local vs. DistributedCells of cortex are arranged in columns

made up of many minicolumns containing:

•neurons receiving subcortical input•neurons receiving input from other areas of cortex (reentrant information)

Vernon Mountcastle: columnar arrangement is a distributed system

information flow follows many different pathways whose dominance at any given time is dynamiccan handle both incoming information and internal (reentrant) information simultaneously


The Cerebral Hemispheres 2 hemispheres

(right/left) connected by bundles of neurons called commissures corpus callosum

largest commissure

allows “cross-talk” severed to control

for severe epilepsy bisected brain

for sensing & moving one hemisphere

controls opposite side of body

= Countralaterality


Hemispheric Specialization left hemisphere (generally)

language & speech (Broca & Wernicke) analytical and sequential

right hemisphere (generally) visual and spatial processing processes information

simultaneously as a whole Face recognition

Left hemisphere controls speech and language in 95% of right handers and 70% of left handers

Not exclusive! – opposite hemisphere also processes


Neurophysiological Sensing Techniques Electroencephalogram (EEG)

•An instrument used to measure electrical activity in the brain through electrodes placed on the scalp

•Shows how long processing takes but not structures, anatomy or functional regions of the brain

•Oldest technique (Hans Berger 1920s)


Neurophysiological Sensing Techniques Computed Axial Tomography (CT)

Rotational X-ray that uses a computer to produce detailed cross-sectional images

Newer versions show internal structures in 3-D and better resolution (clearer pictures)


Neurophysiological Sensing Techniques Positron Emission Tomography (PET)

A visual display of brain activity, as measured by the amount of glucose being used

Radioactive isotopes (small amounts) are placed in the blood.

Sensors detect radioactivity. Active parts of brain require

more blood flow Different tasks show distinct

activity patterns (“map”).


Neurophysiological Sensing Techniques Magnetic Resonance Imaging (MRI/fMRI)

A brain-imaging technique that uses magnetic fields and radio waves to produce, clear three-dimensional images

Now can be used to record rapidly changing functions

fMRI (functional MRI) detects increased blood flow– displays function and structure of brain


Neurophysiological Sensing Techniques

MEG (Magnetoenceohalography) measures the very faint magnetic fields that emanate

from the head as a result of brain activity. MEG provides the most accurate resolution of the

timing of nerve cell activity -- down to the millisecond Produces “activity map” or “functional image”

TMS (Transcranial Magnetic Stimulation) Used with EEG or MEG Evaluates effects of changes in brain electrical

activity in perceiving or thinking Magnetic charge to specific location– effects seen on

EEG or MEG


Cognitive Neuroscience Example 1: Research using PET

Theory = Two separate memory systems (Tulving) Episodic = memory for personal events Semantic = memory for general knowledge

Study: Radioactive tracer into blood stream Blood flow monitored as people think about 2 types of info Found differences in blood flow (so neural activity)

associated with different regions of the brain Episodic: activation in the anterior (front) area Semantic: activation in posterior (back) area

Conclusion: Support for Tulving’s theory– episodic and semantic memory systems involve different brain processes and each has its own location


Cognitive Neuroscience Example 2: Research using PET

Processing of words (Posner & Peterson) Theory = words processed in different areas Study:

Radioactive tracer into blood stream Blood flow monitored as people do four measurements of

activity: Resting (baseline) Viewing word occipital cortex activated Reading word central part of cortex activated Using word associative region + general activation

Conclusion: Each type of word processing uses different parts of the brain.


Cognitive Neuroscience Example 3: Tale of 2 Hemispheres

For Vision information from right

visual field goes to left hemisphere and vice-versa

Can take advantage of this wiring of the visual system with bisected brain patients (cut corpus callosum) to study hemispheric differences

Started 1950’s with work of Sperry and others



Uses a device called a tachistoscope can precisely control location and very brief duration of

stimuli Left hemisphere can say what it saw presented to right visual field Right hemisphere cannot speak, but can retrieve object with left hand

that it saw presented to left visual field



The Z lens (named after creator Eran Zaidel) allows prolonged viewing of stimuli presented to only one hemisphere

with its use discovered right hemisphere language abilities in terms of comprehension roughly equivalent to 10-year-old for single words

Provides support for distributed/parallel processing theory

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Cognitive+Neuroscience