Week 7 Flashcards
(61 cards)
1
Q
Brain imaging assess brain structure and
function “non-invasively” without dissection
or damage to the brain.
True or False?
A
True
2
Q
Neuropsychological methods link function
to brain damage but with no control of
lesion size or location in the brain. So it is
difficult to identify similar patients and
replicate findings – “experiments of nature”
True or false
A
True
3
Q
What is an EEG?
A
EEG refers to both electroencephalography (the equipment/ method) and electroencephalogram (the data output – “writings of electricity from the head”)
4
Q
Who was the first human that tested the EEG
A
Hans Berger (1924)
5
Q
When was the first demonstration of epileptiform spikes with the EEG
A
1934 - Fisher & Lowenback
This is now one of the main diagnostic tests for epilepsy
6
Q
What are some strengths of EEG
A
good temporal resolution (can discriminate very brief
events in time).
- Relatively cheap ($10,000-$100,000 per system). Many psychology departments owning multiple EEG systems
- Portable and possible to record EEG while people are moving around (important in the detection of epileptic seizures that can require people to wear an EEG cap for many days).
- Safe and well tolerated by participants - no real risks associated with placing recording electrodes on a person, beyond mild discomfort.
7
Q
What are some limitations of the EEG
A
- Poor spatial resolution. With more electrodes the spatial resolution can be improved, but it still difficult to determine precisely from which area of the underlying brain the signal has come.
- Typically only detects activity on the surface of the cortex. It is very hard to detect activity from more central regions within the brain, as the electrodes are attached to the outside of the scull.
8
Q
____________ recorded action
potentials (electrical signals) in
the giant axon of Atlantic squid in
_____ (won Nobel prize in 1963)
A
Hodgkin & Huxley recorded action
potentials (electrical signals) in
the giant axon of Atlantic squid in
1952 (won Nobel prize in 1963)
9
Q
A subsequent explosion of
research in the following decades
was based on technical advancements
What were they?
A
- Development of microelectrodes
- “multi-unit” recording electrodes
10
Q
_________ mapped the development and functional organisation of the
visual system (won Nobel prize in 1981)
Electrophysiology – Single Neurons
A
Hubel & Wiesel
11
Q
What are strengths of Electrophysiology
A
Records directly from individual neurons so is the best method to use if you want to know what the neurons are doing
12
Q
What are limitations of Electrophysiology
A
- High risks of infection as this technique is “invasive” penetrating the brain.
- It is only possible to record from a few (up to ~ 100 neurons at a time with multielectrode arrays), so can only record individual neurons or small network activity.
13
Q
What is Magnetic Resonance Imaging (MRI)
A
- MRI exploits the magnetic properties of brain tissue.
- MRI coil generates a VERY strong magnetic field (The earth’s magnetic field is about 1/1000 tesla, whereas the field created by an MRI scanner is between 1.5 and 7 tesla).
14
Q
How does an MRI do structural imaging?
A
- Magnetic field passes through the person’s head causing hydrogen atoms to align with the magnetic field.
- Radio frequency waves temporarily disrupt this alignment causing a signal that can be detected by this machine.
- Because different areas of brain tissue contain different amounts
of water (H2O), they emit different signals. - Analysis software converts detected signals into very detailed images of different structures in the brain.
15
Q
What/How is Diffusion Tensor Imaging work?
A
Diffusion Tensor Imaging (DTI) – uses the same MRI equipment to detect the large axon tracts (“white matter”) that flow through the brain and connect different regions of cortex
16
Q
What is fMRI- Functional Imaging
A
Cognitive processes use energy
The production of energy uses oxygen from hemoglobin (blood)
17
Q
Oxygenated Blood distorts the magentic field
True or False
A
False
Oxygenated blood doesn’t distort surrounding magnetic field
18
Q
Deoxygenated Blood doesnt distort the magentic field
True or False
A
False
Distorts surrounding magnetic field
= blood vessels became more visible as blood oxygen decreased
19
Q
What is the Blood-oxygen-level-dependent (BOLD) signal?
A
Blood-oxygen-level-dependent (BOLD) signal tracks the ratio of oxygenated vs deoxygenated blood
20
Q
BOLD dominates fMRI studies that
map human brain function
True or False?
A
True
21
Q
How does BOLD dominate fMRI studies
A
As the brain region uses energy
there is an increase in blood flow to
the region.
- Because fMRI images reflect the
change in oxygen levels in the blood
(not the neurons directly) there is a
delay of a few seconds between
time of neural activity and change in
blood oxygen levels.
22
Q
What are the strengths of MRI
A
- Very high spatial resolution, identifying exactly where in the brain different structures are or different function is occurring.
- MRI is also a very valuable tool because it can identify
specific anatomical/Structural and functional properties of different brain regions.
23
Q
What are the limitations of MRI
A
- MRI machines are very expensive and can cost ~$1million for the latest equipment.
- The equipment is also very large equipment and requires a specialist facility with multiple rooms to enable
staff to work and the machine to be kept within a magnetically shielded room. - Some safety risks associated with the large magnet, so it is
important to ensure that no metal enters the MRI room. - Requires specialist staff with radiography training (due to
the cost and safety concerns)
24
Q
What is Position Emissions Tomography (PET)
A
- Uses radioactive substances
knowns as tracers to visualise
glucose metabolism or the
neurotransmitter/ receptor
function
25
What is PET used for?
PET is currently used as a diagnostic tool for Alzheimer’s Disease (detecting buildup of Amaloid protein)
Can also use radioactive tracers to bind selectively to proteins of interest.
26
What are the strengths of PET?
Can detect different chemicals in the brain associated with either the metabolism (energy consumption), or specific neurotransmitter levels or receptors
27
What are the limitations of PET
- Expensive and requires specialist facilities and staff
- Relatively low spatial resolution compared to MRI
- The signal requires radioactive tracers to be injected into a
participant’s blood (it is considered very safe, but it is important that the risks are managed with the appropriate safety precautions)
28
What can Brain modification be used?
Using different methods brain
regions can be permanently
removed/destroyed or the brain
activity can be temporarily
decreased.
OR
* Brain areas can also be
stimulated to enhance or
increase brain activity in that
region
29
How can brain modification be used as medical treatment?
Many psychiatric and neurological conditions are associated
with abnormal brain functions. Treatment of these disorders
will often target the abnormal brain processes involved.
- In some cases, such as epilepsy or brain tumour, treatment
might involve removal of sections of abnormal brain tissue.
- Drugs can also be used to selectively target abnormal function
of specific neurotransmitter systems
30
Explain Brain Modification for enhancement
Refers to the improvement of healthy function to above or better than
normal. In contrast to medical use, which aims to improve impairments
to achieve healthy function.
Brain Modification - Introduction
- There is increasing claims around the use of both brain
stimulation and drugs to improve brain function beyond typical
normal levels.
- This is an area that has attracted a lot of attention from
neuroethicists.
31
Explain Brain modification for scientific research
- Brain modulation techniques offer powerful tools for research.
- Unlike brain imaging techniques like fMRI which provide correlational
information, brain modulation provides information about causation
and whether a given brain region is necessary for a particular task.
- In the past, naturally occurring brain damage has provided
information about the role of different brain areas (i.e. Broca’s area in language production). New techniques to modify specific brain
regions or process in living people, make it possible to test hypotheses and directly examine the links to behaviour
32
What is ablation?
The term ablation = “to carry away”
- Deliberate lesions allow a relatively
high degree of precision
- For research purposes this was
limited to animal studies. Human
ablation was used for medical
treatment.
33
Who introduced Surgical ablation
Portugese physician Egas Moniz introduced the prefrontal leucotomy for the relief of psychiatric disorders
34
What did prefrontal leucotomy explain?
- This worked linked personality to the frontal lobes
- Based on reports that removing the frontal lobes
of a chimpanzee made it calmer and more cooperative
- While results for patients were not always positive, clinician’s at the time considered the procedure successful
- Moniz awarded Nobel Prize for this discover
35
What are two methods for frontal Leucotomy?
- A leucotome was inserted into one of several holes drilled in the skull. The wire was then extruded from the tip and the leucotome rotated to remove a core of tissue.
- Alternatively, a cutting implement was inserted above the eyelid, pushed through the base of
the skull (which is very thin and brittle just above the eyes), and rocked from side to side to slice through the frontal lobes, thus
separating them from the rest of the brain.
36
What are profound personality consequences of frontal leucotomy?
- Apathy
- Emotional unresponsiveness
- Disinhibition
- Inability to plan
37
Who popularised frontal leucotomy?
Popularised by Walter Freeman in
the 40’s and 50’s
- 40,000 operations in the USA
38
What were the initial impressions of the improvements made by frontal leucotomy?
- Led to its widespread use
- Subsequently shown to be ineffective
39
What is electrical brain stimulation?
Electrical stimulation has also been used to reveal precise localisation of cortical function.
- In 1870, Fritsch & Hitzig (Germany) electrically stimulated part of the frontal cortex in dogs;
induced contractions of specific muscles on the opposite side of the body
40
What is Non-invasive electrical brain stimulation (ECT)
- Electroconvulsive Therapy (ECT)
invented in Italy in the 1930s
- It was already known that seizures
reduced psychiatric symptoms
As early as the 1500s, seizure inducing agents were used to treat psychiatric conditions
- ECT originally used to treat a range of mental illnesses
- Now used to treat severe depression
- Mechanism of action is unknown
electrical stimulation of the frontal lobes needs to be strong enough to cause a seizure
41
What are Non-invasive electrical brain stimulation? (tDCS)
A range of non-invasive methods for
electrical brain stimulation now exist,
however the efficacy and safety
remains debated.
The most common method is
transcranial direct current stimulation (tDCS).
42
How does Transcranial Magnetic stimulation (TMS) work?
In Transcranial Magnetic stimulation (TMS), a coil carrying an electrical
current generates a brief, focal magnetic pulse which activates a small region of cortex (approximately 10 – 15 mm) underlying the coil.
- The activation acts like a ‘virtual lesion’, temporarily disrupting the tissue for a few hundred milliseconds. The technique is painless (unless it triggers
muscle contraction).
TMS is a non-invasive magnetic brain stimulation - TMS
43
How does drugs influence brain modification?
Drugs can impact every stage of neurotransmitter function from synthesis to release to receptor binding
44
What are features of synaptic plasticity?
The brain is always active (even in sleep).
- The pattern of activation of neurons can itself impact future
activation of neurons.
- The adaptability/changeability of neural connections is
referred to as synaptic plasticity.
- Existing synapses can be strengthened or weakened (see
next slides)
- New synapses can be generated existing synapses can shrink or be removed
45
What is Long Term Potentiation (LTP)
If activation at one synapse is repeatedly accompanied by an
action potential at the post synaptic neuron, the synaptic
connection becomes stronger.
- The post synaptic neuron will become more “sensitive” to
neurotransmitter release from presynaptic neuron and more
likely to reach the threshold for activation.
- Increasing the likelihood of a post-synaptic potential allows the neural signal to be transmitted more quickly (remember the “rate law”).
- Important in learning (and motor speed that comes with
practiced movements).
- Long-Term Potentiation (LTP) referred to as either the Hebb
Rule or Hebbian Learning in recognition of Donald Hebb’s
1949 proposal that “neurons that fire together wire together.”
46
What is Long Term Depression (LTD)
- Long-term depression (LTD) can be broadly conceptualised as the opposite of LTP with weakening of synaptic connections.
- The post-synaptic neuron becomes less sensitive to
neurotransmitter release by the presynaptic neuron and will be
less likely to fire in response.
- Memories can fade and skills can be lost if the underlying neural networks are not stimulated sufficiently - “use it or lose it.”
- It is an important complement to the strengthening of synaptic
connections in LTP and weakens synaptic connections that are infrequently stimulated.
- LTP & LTD together enable the brain to adapt to current needs
47
What is Neurogenesis?
- Was thought brain is unable to generate new neurons and that
dead neurons would never be replaced.
- Now clear that new neurons can be generated through a
process – termed neurogenesis.
- Importantly, this process is
largely restricted to the
Hippocampus (involved in
the consolidation of long-
term memories) and the
olfactory bulb (involved in
detection of odour/smell)
48
What is the bad news about synaptic plasticity?
Synaptic plasticity often presented in the media and “self- help” books as capacity for the entire brain to totally
transform and replace damaged brain tissue as needed. Unfortunately, that is not true.
- Neurogenesis does not occur in all brain regions.
- People typically experience some degree of sustained
impairment after severe stroke or traumatic brain damage.
- The neurons that are destroyed are typically not replaced in the brain and
function will remain impaired
49
What is the good news about synaptic plasticity?
- Thanks to LTP & LTD, there is tremendous capacity for surviving neurons to adapt, increasing connections between healthy brain regions > weakening or removing connections with damaged
areas.
- This leads to improved
function and
rehabilitation through
“retraining” their brain to
compensate for some
lost functioning.
50
What is functional connectivity?
To understand the relationship between brain and mind we
must consider
51
Provide an example of motor control work?
Whether crossing a road or trying to hit a cricket ball the brain is required to
integrated information from different regions within the brain that are specialised for different functions.
52
How does Motor control work
1. Consider the case of hitting a cricket ball.
2. Eyes and ears provide important visual and auditory cues.
3. Some sensory signals may be
important for successful execution of the
task other signals might be distracting
(such heckling from the opponent).
4. The brain must select the relevant sensory cues depending on the current task or goals which are maintained in working memory and supported by the frontal cortex.
5. Appropriate motor actions need to executed, balance maintained etc etc
Everything must happen quickly!!
53
What is Emotion?
The concept of emotion has several different
meanings:
- positive or negative feelings we experience (happiness, fear, etc).
- Emotion can also be used to refer to the physiological or behavioural changes (increase in heart
rate, rapid breathing, eye gaze etc.
Emotions consist of patterns of physiological
response and species-typical behaviours.
In humans these physiological responses are
accompanied by feelings.
Feelings are powerful motivators
Emotions are likely to have evolutionary
significance (Charles Darwin;1872)
54
What are the three components of emotional responses?
- Behavioural
- Autonomic
- Hormonal
55
What is the behavioural component of the emotional response?
Muscular changes that are appropriate to the situation that elicits them
56
What is the autonomic component of the emotional response?
Physiological changes induced by the autonomic nervous system facilitate the behavioural responses.
57
What is the hormonal component of the emotional response?
- Within the body hormones reinforce the
autonomic changes.
- The adrenal gland secretes adrenaline.
- Adrenaline acts to further increase blood flow to the muscles and cause nutrients
stored in the muscles to be converted into glucose.
58
What is integration in emotional responses
- The three components of the
emotional responses
(Behavioural, Autonomic and
Hormonal) involve separate
aspects of the nervous
systems.
-The amygdala plays an
important role in coordinating
the emotional response and
sending the appropriate signals
to the autonomic and hormonal
responses.
59
How do emotional response integrate in the cricket example
In the cricket example, if player is nervous this will increase noradrenaline release.
1. Noradrenaline increase the player’s heart rate (and other impacts of sympathetic
nervous system activation).
2. Within the brain this heighten emotional responses might lead to impulsive decisions
and introduce errors.
3. In the context of a person running from a lion, the benefit of increased speed greatly
outweighs the potential negative consequences of reduced accuracy.
4. In the context of a cricket game (or a university exam) where life is not in threat, a
calm head may be better for deliberate strategic decisions and reduced errors.
Emotional responses help to integrate incoming sensory signals and coordinate
appropriate regulation of the brain and body. The purpose of the emotion is to modify a person’s experience and behaviour in a way that is appropriate for the
context.
60
How does the lie detector (polygraph) work
Emotional reactions to questions are used to
determine ‘truthfulness’ of answers
- Measures physiological responses
associated with activity of autonomic nervous
system
- Still used routinely by law enforcement authorities in many countries
61
What is consciousness?
It remains clear that different regions of the brain do different things
- It is also very clear that the different brain regions are highly integrated through a highly complex network of
neural connections
- Understanding this complex
connectivity is a major current goal of neuroscience
- Understanding how brain activity supports subjective/conscious experience of the mind remains a
mystery
