16) Investigating the brain Flashcards
When were post mortems used
19th & 20th century
Where is Brocas area
left frontal lobe
Broca’s area function
speech
brief NS structure (microscopic analysis of neural tissue)
6 layers of neocortex (brain cortex) found by Brodmann
two examples of structural imaging
CT scan
MRI
CT scan
Computerized tomography
MRI
magnetic resonance imaging
CT scan explained
contrast dye injected into blood
xrays taken from different angles
scanner rotates to measure these angles
radiation absorption varies with tissue density
computer constructs images of the brain
MRI explained
magnetic field 25000 times greater than that of earth
brain atoms release electromagnetic energy
£D image of brain created
EEG
Electroencephalography
EEG explained
Electrical brain activity measured on scalp
sensitive to post synaptic dendritic currents generated by synchronised active neurons
strength of EEG
excellent temporal resolution (<1ms)
weakness of EEG
poor spatial resolution - scalp signal is sum of signals from diff sources (locations cant be accurately inferred)
Hans Berger 1929
first to record electric potentials from brain on scalp using EEG
Nervous system activity (impulses) (5)
Delta, Theta, Alpha, Beta, Gamma
Delta
0.5 - 4Hz
sleep
theta
4-7Hz
sleep
meditation
excess theta for age-abnormal activity due to focal subcortical lesions
alpha
8-12Hz
relaxation
beta
12-30Hz
alertness, attention, REM sleep
Gamma
30-100Hz
Phineas Gage
damage to ventral part of PFC
intact speech and movement
disinhibition of innappropriate behaviour
brain damage trials
patient with amygdala dysfunction in limbic system drew six emotions - for ‘afraid’ they drew baby not expression
effects of brain surgery
mechanical brain injury
stroke
chemical poisoning
neuropsychological test batteries
mapping brain function
electric brain stimulation (in vivo) conscious patients during surgery
stimulate areas and see what responds
eg i feel something on my hand or hear something etc
single cell recordings
neuron behaviour examined through micro electrodes
records electrical activity of single neuron (but doesn’t stimulate)
animal study - cat
Hunsperger & Bucher (1967)
brain electrical stimulation in cats - current provoked expression change
and lesion studies
animal lesion studies
deliberately damage or remove specific brain regions and then observe cognitive function and behaviour
TMS
Transcranial magnetic stimulation
strength of TMS
non invasive
TMS explained
neurons excited or inhibited by externally applied time-varying electromagnetic fields, generated by coil above head
ERP
Event related potentials
ERP explained
EEG recording during cognitive task
activity time-locked to external event (eg sound)
peak direction (pos/neg) amplitude and timing used to investigate brain process in diff cognitive domains
three examples of brain damage case studies
phineas gage - frontal lobe damage
corpus callosotomy
brocas aphasia
corpus callosotomy
cannot say what object they are holding because RH receives info from hand and LH verbalises the info (same results for visual/verbal info)
brocas aphasia
patients with lesions to brocas in LH (left ineferior frontal gyrus) have telegraphic speech
telegraphic speech
two word sentences
Quiroga (2005)
single cell recordings in hippocampus that recognise specific people
ERP components
N100
N170
N100 (ERP)
responds to sounds from auditory cortex (attenuates as listener habituates)
N170 (ERP)
relatively specialised for facial recognition
MEG
Magnetoencephalography
MEG explained
recording of magnetic fields produced by electrical currents in the brain using arrays of SQUIDs
SQUIDs
superconducting quantum interference devices
MEG qualities
signal unaffected by skull, meninges
more sensitive to activity at sulci
ms temporal resolution
potentially good spatial resolution (2-3mm)
expensive and limited availability
EEG/ERP qualities
signal affected by skull, meninges
sensitive to gyri and sulci activity
ms temporal resolution
poor spatial resolution
cheaper and widely available
meninges
protect the brain and spinal cord
functional imaging
measures neuronal activity - eg brain activity associated with cognitive processing
2 examples of functional imaging
fMRI
PET scan
fMRI
functional magnetic resonance imaging
fMRI explained
measures activation by detecting the increase in oxygen levels
active neurons consume oxygen and convert oxyhaemoglobin into deoxyhaemoglobin
measure conc of (de)oxyhaemoglobin in the blood - as in the BOLD response
BOLD response chnage over time shows hemodynamic response function
hemodynamic response function
allows localisation of active voxels
peaks in 6-8 seconds after event and is extended over time - limiting temporal resolution of fMRI
BOLD response
blood oxygen level dependent contrast
voxel
cube/cuboid of brain tissue
Wagner (1998)
fMRI of word processing:
indicated areas (posterior LIFG, anterior LIFG and fusiform gyrus) more active when words being processed were later recalled, than those that weren’t
PET scan
Positron Emission Tomography
PET explained
measures local blood flow into a brain region
radioactive tracer injected into blood stream
tracer takes 30 seconds to peak
PET qualities
based on blood volume
radioactivity involved
temporal res: 30sec
effective spatial res: 10mm
sensitive to whole brain
fMRI qualities
based on blood oxygen conc
no radioactivity involved
temporal res: 1-4sec
spatial res: 1mm
some brain regions hard to image (near sinuses)
(lack of precision)
neuroanatomy of corpus callosum
brain stem
> 200 million axons
wide connectivity with entire cortex
most regions send/receive axons through cc
5 regions of the corpus callosum
rostrum
genu
body
splenium
anterior commissure
epilepsy explained
large electrical discharge in focal area then spreads through brain
generalised Grand Mal drops seizures are potentially dangerous as they can lead to further injuries
surgical intervention for epilepsy
separation of the brain hemispheres
split brain surgery
what affliction does split brain surgery rectify
epilepsy and grand mal seizures
modern split brain methodology - using visual pathway
visual info is proceeds to the contralateral hemisphere
hemispheric transfer necessary for each hemisphere to perceive ipsilateral space and for midline fusion
contralateral
opposite
lateral and medial pathways - modern split brain methodology (visual pathway)
contralateral control of distal effectors
ipsilateral control of proximal effectors only
can therefore use unilateral inputs and unilateral response to measure hemispheric function
ipsilateral
same side of body
unilateral
affects only one side
Gazzaniga (1962)
first study to show lateralised differences in WJ (patient)
- split brain study
left hemisphere
speech/language
problem solving
arithmetic
generis processing (interpreting the world)
maybe more dominant
right hemisphere
visuospatial abilities
perceptual grouping
face processing
veridical processing
(higher order perceptual interpretation)
veridical processing
direct perception of stimuli as they exist (congruent with reality)
