PSYCH 109 - Brain and Language

neurons

perform computations (thought) in the brain, form complex connections with other neurons

parts of a neuron

• dendrites

• cell body

• axon

• axon terminals

dendrites function

receive nerve impulses from other neurons

cell body function

responsible for metabolism and maintenance of the cell

axon function

transmit nerve impulses and carry action potential

axon terminal function

secrete neurotransmitters into synapse

motor neuron

begin in central nervous system, exit through spinal cord, end on muscle fibre. responsible for movement and motor actions

sensory neuron

begin at sense organ (retina, skin, tongue), convey information to brain via spinal cord

interneuron

interposed between other neurons, do much of the computation in the brain

glial cell

around 90% of cells in the brain. act as guidewires for growing neurons, later in development provide scaffolding for mature neurons and assist in repair when tissue is damaged

myelinated axons

white matter, nerve impulse travels faster (20m/s)

unmyelinated axons

grey matter, nerve impulse travels slower (1m/s)

resting potential of a neuron

the inside of an axon is negative with respect to the surface, by about -70 millivolts

action potential of a neuron

when a pulse is applied that exceeds the excitation threshold, about -55 millivolts, causes the inside to swing positive relative to the outside

how action potential occurs

• ingoing channels open, Na+ ions pour into the cell, reversing voltage difference

• Na+ channels close, K+ ions go outside the cell

• Na+ pushed outside the cell, K+ drawn inside (returned to original levels)

synapse

where one neuron meets another. transmission of an action potential along one neuron may cause the next neuron to fire (excitation) or it may inhibit firing (inhibition). governed by the release of neurotransmitters

parts of a synapse

• pre-synaptic membranes

• post-synaptic membranes

• synaptic gap

• synaptic vesicles

synaptic reuptake

neurotransmitters don’t sit in the synapse: inactivated by “clean-up” enzymes and reused

drugs and the synapse

1. stimulate or inhibit neurotransmitter release

2. stimulate or block post-synaptic receptor molecules

3. inhibit reuptake

how to study the brain

we want to measure what we can from the brain, as related to activity associated with behaviour or process, non-invasively and in-vivo

Electroencephalography (EEG)

measurement of differences in electrical activity across the skull to make inferences about the underlying cortical structure. involves using electrodes embedded in cap with gel applied to improve connection between head and electrodes

what EEG actually measures

• signal + noise

• signal: the electrical activity related to a process or cognition

• noise: the electrical activity related to everything that’s not the signal

• it does not measure thoughts or structures of the brain, it measures specific neurons in specific circumstances

EEG in application

• investigating the processes that underly cognition e.g. predicting people’s preferences

• recordings can help with identification and study of epilepsy

• useful for research on stages of sleep

• use of EEG to find markers of psychiatric disorders

EEG strengths and weaknesses

strength: great temporal resolution, really good for questions about when processes are occurring. weakness: bad spatial resolution, we don’t know for certain what is driving that activity

Magnetic Resonance Imaging (MRI)

generates an image of the structure of the brain. useful for research and for detecting brain abnormalities

MRI scanner

essentially a very large magnet, anywhere from 1.5T to 3T is common. image resolution is dependent on magnet strength and size of voxels

what MRI actually measures

• protons are spinning around on axis with random orientation within brain tissue

• MRI scanner magnet applied which aligns orientation of protons

• external radio frequency pulse un-aligns protons from magnetic field

• as protons re-align, they release energy that is recorded by scanner

• different tissues have different concentrations of hydrogen protons and look different on the scan

Functional Magnetic Resonance Imaging (fMRI)

shows functional representation of what is going on in the brain, where specific cognition is located

what fMRI actually measures

• neuronal activity causes localised changes in blood flow

• higher activity → increased demand for oxygen → increased blood flow and oxygen-laden haemoglobin

• magnetic properties for oxygenated and deoxygenated haemoglobin differ

• this gives us BOLD (Blood Oxygen Level Dependent) signal

MRI/fMRI strengths and weaknesses

strengths: spatial resolution, useful to see differences in structures (MRI) or activity in certain structures (fMRI). images can be very high resolution with small voxels and strong magnetic field. weakness: bad temporal resolution making it difficult to link structure to behaviour/cognition in real time (fMRI)

MRI/fMRI difficulties

• need to be near a scanner

• need to be able to afford to use it

• various sources of ‘noise’ that need to be taken into account

MRI/fMRI applications in research

• activity related to behaviour

• co-activation - two regions active at the same time

• networks - one region active and other region loses activity, shows organisation of brain

• activation of regions shows evidence of depression

central nervous system

brain and spinal cord

peripheral nervous system

1. somatic nervous system - afferent, efferent and cranial nerves

2. autonomic nervous system - regulation of viscera i.e. heart, lungs, blood vessels, digestion, sex organs

afferent nerves (sensory)

transmit information from sense organs to brain and spinal cord

efferent nerves (motor)

transmit information from central nervous system to effectors (muscles/glands that are the organs of action)

cranial nerves

• 12 pairs, enter/exit from hindbrain

• poke through holes in skull - afferent/efferent functions

• control movements of and carry sensations from head and neck e.g. seeing, smelling, hearing

• regulate glandular secretions in head e.g. tears, saliva, mucus

• control visceral functions e.g. digestion, secretion

Bells Palsy

• related to cranial nerves

• issues with face - droopy, one-sided, cannot smile, cannot blink

• unknown cause and variable recovery period

• may need psychological support

Trigeminal Neuralgia

• related to cranial nerves

• incredibly severe facial pain

• not well controlled by painkillers

• may need psychological support - colloquially known as ‘suicide disease’ 

Photic sneezing

• function of cranial nerve

• causes people to sneeze when they look at bright lights

• genetic, not a result of damage

human vs animal brain similarities

• all have left and right hemisphere

• all have split between hemispheres (longitudinal fissure)

• all have hindbrain areas i.e. cerebellum

human vs animal brain differences

• animals (rats, rabbits) have large olfactory bulbs at the front of their brain due to importance of smell sense, humans have small olfactory tracts hidden underneath brain

• animals (rats, rabbits) have smooth brains, humans have wrinkled cerebral cortex as we have more complex cognitive abilities

human brain sections

• two hemispheres

• hemispheres are anatomically similar but functionally different

• left hemisphere dominant for language, right hemisphere dominant for spatial awareness

• brain divided into three major parts - hindbrain, midbrain, forebrain (cortex)

pons (hindbrain) function

• arousal (consciousness)

• relays sensory information between cerebellum, cerebrum and other parts of brain

• regulates respiration

• involved in sleep and dreaming - shuts down muscles

pons (hindbrain) damage

• damaged pons in cats caused them to move around when asleep

• damaged pons can cause Locked-in Syndrome - completely paralysed apart from eye muscles

medulla (hindbrain) function

• regulation of heart rate, blood pressure, rate of respiration

• involved in vomiting, defecation, reflexes, swallowing

• in simpler animals it is involved in crawling/swimming motions

medulla (hindbrain) damage

• damage can cause death

• no control over swallowing reflex can mean food/drink easily goes down windpipe

cerebellum (hindbrain) function

• knows what each part of body is doing

• receives information from frontal lobes, knows what movements lobe intends to do

• monitors information about posture/balance, produces eye movements to compensate for head position changes

• may play a role in learning new movements/skills

• very well developed in humans and primates

cerebellum (hindbrain) damage

• injury, disease or alcohol can cause wide stance and staggering gait

• damage can cause tremors during movement and inability to perform rapidly alternating movements

• damage impairs thinking and performance of tasks requiring exact sequencing

the midbrain

• auditory and visual stimuli - eye movement

• control movements used in sexual behaviour and fighting

• decrease sensitivity to pain

• midbrain in floppy-eared rabbits causes ears to prick up/move

• midbrain in birds of prey help them to scan environment and quickly swoop down and catch prey

the forebrain

• everything above midbrain

• mammals have largest forebrains

• human forebrain is so large it hides midbrain and half of hindbrain

• has wrinkled cortex - outer layer of brain, most important for psychological functions

meninges

three layers:

• dura - tough external wrap

• arachnoid - more flimsy

• pia mater - most flimsy, closest to cerebral cortex

cortex size

in primates/complex mammals it is more than ½ brain’s volume (80% in humans). cortex is 2-3mm thick and very convoluted

cortex function

tasks performed by limbic system/midbrain in non-mammals are performed by cortex in mammals. as cortex enlarged, midbrain acts more as relay station. cortex allows for large flexibility in behaviour

gyrus

ridges, protruding parts of cortex. responsible for controlling function

sulcus

grooves or fissures between ridges. no function, just landmarks

thalamus (subcortical forebrain)

receives sensory information from sense organs, performs simple analyses and passes results on to primary sensory cortex

hypothalamus (subcortical forebrain)

homeostasis and species typical behaviours. feeding, drinking, body temperature, sex. controls much of activity of Autonomic Nervous System

basal ganglia (subcortical forebrain)

regulation and smoothing of movement

damage to basal ganglia

degenerative diseases:

• Parkinson’s - movement affected by shaking, unexpressive face

• Huntington’s - genetic disease of writhing muscles

• Foreign Accent Syndrome - accident/stroke results in different accent

hippocampus (subcortical forebrain, limbic system)

important for forming memories

amygdala (subcortical forebrain, limbic system)

allows us to experience emotion, form facial expressions, and interpret others’ facial expressions

damage to amygdala

Capgras Syndrome - people believe their close acquaintances are imposters impersonating them. they can recognise faces but have lost emotional connection and physiological reaction so they believe it’s not them

four lobes of cortex

occipital, parietal, temporal, frontal

occipital lobe

back of the brain. receives input from eyes via thalamus, interprets and comprehends visual environment

parietal lobe

important for spatial perception. contains postcentral gyrus, receiving area for skin senses

temporal lobe

receiving area for auditory information. role in memory. processes olfaction (smell), can connect smells with memories

frontal lobe

responsible for motor output and motor planning. contains precentral gyrus - maps onto movements of different parts of body

primary areas

basic input (sensory) and output (motor), no computation/interpretation

association areas

for elaboration or “higher functions”

primary motor area

very specific effects when electric currents applied to specific areas of cortex. evidence of contralateral control i.e. area in left hemisphere controls right hand

Brodmann areas

specific areas of specific function

homunculus of primary motor cortex

mapping body surface onto motor cortex - body parts requiring more movement are allocated more space on cortex. mapped upside down

homunculus of primary sensory cortex

mapping body surface onto sensory cortex - body parts more sensitive to touch receive more cortical space. mapped upside down

damage to primary visual cortex

• scotoma - hole in visual field, blind spot

• removal on one side → hemianopia (loss of vision) on other side

damage to primary motor cortex

• hemiplegia - paralysis on one side of body

• paralysis worse at extremities

prosopagnosia

damage to temporal/occipital lobes. results in difficulty recognising faces, some can’t recognise a face as a face

damage to prefrontal cortex

• deficiency in response inhibition

• inability to plan / lack of foresight

• some uninvolved, apathetic, depressed, some flagrant, crude, criminal

• problems with initiating behaviour / changing strategies

Phineas Gage

a man who suffered damage to prefrontal cortex after accident with explosives causing iron rod to go through head. his personality was dramatically altered from pleasant, quiet person to aggressive, profane person

prefrontal lobotomy

surgeries in 1940s-50s that disconnected prefrontal areas. helped some, but used indiscriminately. patients ended up docile but cognitively disabled

apraxia

damage to frontal lobe causes serious disturbances in inaction or organisation of voluntary actions. unable to perform well-known actions and actions become fragmented

neglect syndrome

people with right-sided parietal damage tend to neglect left side of space (seldom vice versa). can be visual, auditory, tactual. problem of attention. sometimes denial of any deficit (anosognosia)

right hemisphere of brain

dominant for spatial attention (neglect), melody (amusia), facial recognition (prosopagnosia), recognition of natural objects (agnosia)

left hemisphere of brain

dominant for language (aphasia), recognition of manufactured objects (agnosia), voluntary action (apraxia)

split-brain surgery

relief of intractable, multi-focal epilepsy. separates lefts and right hemispheres and prevents seizures from spreading through brain

corpus callosum

largest cerebral commissure (communicating pathway), over 200 million myelinated axons. lies beneath longitudinal fissure

commissurotomy

in 1960s all forebrain commissures were sectioned

callosotomy

1970s onwards only some of corpus callosum was sectioned. done in two stages - first anterior, if that doesn’t work then posterior also

effectiveness of split-brain surgery

successful in controlling epilepsy. surgery reduced in frequency with better drugs and more understanding of psychological effects

what the split-brain tells us

split-brain patients seem quite normal - psychological effects are best shown by experiment rather than everyday life. rare effect of “alien hand”, an autonomous, uncontrolled hand 

“disconnection syndrome” visual techniques

best addressed through vision, since visual fields are split cleanly through vertical meridian

left hemisphere function in split-brain

• can’t name objects or words presented left visual field

• can’t name objects held in left hand

• but can understand words in left visual field

• suggests that right brain can understand but not speak

callosal agenesis

• people who are “naturally” split-brained because corpus callosum did not develop

• sometimes accompanied by Probst’s bundles, remnants of corpus callosum that failed to develop

• condition often accompanied by other neurological problems, but otherwise seem normal

• less evidence of hemispheric disconnection than surgery - interhemispheric transmission time around 20-30ms, compared with normal 4-6ms

neural plasticity

evident in those with callosal agenesis. if born without corpus callosum, you form other neural pathways. evidence of plasticity in surgical cases done before puberty

Whorfian hypothesis about language

language shapes thought and thought shapes language. language evolves to express new concepts/ideas

what is language?

• system of symbols, sounds, meanings and rules

• system constitutes primary mode of communication among humans

• use phonology and morphology to transform sounds into meaningful words

• use grammatical rules to transform sounds into meaningful sentences

four aspects of language

• phonology

• syntax

• semantics

• pragmatics

phonology

phonemes: basic perceptual units of speech, combined with others to make meaning. not the same as letters

graphemes: letters

phonology decoding

detecting speech features and categorising the sound as phoneme

speech perception

sounds of language are heard, interpreted and understood. fast speed of speech signal - in regular conversation it’s hard to distinguish phonemes