| How does transcranial magnetic stimulation (TMS) work? | A coil carrying an electrical current generates a brief, focal magnetic pulse which activates a small region of cortex underlying the coil.
Activation acts as a "virtual lesion", temporarily disrupting the tissue for a few hundred milliseconds.
Painless process. |
| What is the aim of brain imaging? | To assess brain structure and function "non-invasively" without dissection or damage to the brain. |
| What is electroencephalography (EEG)? | EEG refers to both electroencephalography (equipment/method) and electroencephalogram (data output/"writings of electricity from the head"). |
| Give an example of when EEGs are used. | To diagnose epilepsy. |
| What are the strengths of EEG? | Good temporal resolution (i.e. discriminate very brief events in time).
Relatively cheap ($10,000-$100,000 per system).
Portable and possible to record EEG while people are moving around (e.g. detection of epileptic seizures that can require people to wear an EEG cap for many days).
Safe and well tolerated by patients - no real risks.
Patients have few concerns about the technology. |
| What are the limitations of EEG? | Poor spatial resolution - with more electrodes the spatial resolution can be improved by still hard to determine precise location of where the brain signal has come.
Typically only detects activity on the surface of the cortex - hard to detect activity from more central regions within the brain as electrodes are attached to the outside of the skull. |
| What are the strengths of electrophysiology (single neurons)? | Records directly from individual neurons - best method to use if you want to know what the neurons are doing. |
| What are the limitations of electrophysiology? | High risks of infection as this technique is "invasive" as it penetrates the brain.
Neurons often don't work in isolation, so cannot use this method to investigate network activity of multiple neurons. |
| What does magnetic resonance imaging (MRI) utilise? | Exploits the magnetic properties of brain tissues. |
| How does MRI work? | MRI coil generates a very strong magnetic field.
Magnetic field passes through the person's head causing hydrogen atoms 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, they emit different signals.
Analysis software converts detected signals into very detailed images of different structures in the brain. |
| What is diffusion tensor imaging (DTI)? | Used for structural imaging.
Uses the same MRI equipment to detect the large axon tracts ("white matter") that flow through the brain and connect different regions of cortex. |
| What does fMRI measure? | Provides functional imaging.
Measures the small changes in blood flow that occur with brain activity. |
| Explain the processes involved in fMRI. | Cognitive processes use energy - this production of energy uses oxygen from haemoglobin (blood).
Oxygenated blood - doesn't distort surrounding magnetic field.
Deoxygenated blood - distorts surrounding magnetic field.
Blood vessels are more visible as blood oxygen decreases. |
| What is the most popular version of fMRI? | Blood-oxygen-level-dependent (BOLD). |
| How does BOLD fMRI work? | As the brain region uses energy, there is an increase in blood flow to the region.
Because fMRI images the increase in blood flow caused by the use of the oxygen - there is a delay in signal associated with brain activity. |
| What are the strengths of MRI? | Very high spatial resolution - identifies exactly where in the brain different structures are or different function is occuring.
Can identify specific anatomical/structural and functional properties of different brain regions. |
| What are the limitations of MRI? | Very expensive - machines cost ~$1million.
Equipment is very large and require a specialist facility (magnetically shielded room).
Safety risks (no metal).
Specialist staff required (radiography training). |
| What does positron emissions tomography (PET) do? | Uses radioactive substances (tracers) to visualise glucose metabolism or the neurotransmitter/receptor function.
Can also use radioactive tracers to bind selectively to proteins of interest. |
| What is PET used as a diagnostic tool for? | Alzheimer's disease - detects build up of Amaloid protein). |
| What are the strengths of PET? | Can detect different chemicals in the brain associated with either the metabolism (energy consumption), or functional properties such as specific neurotransmitters levels or proteins. |
| What are the limitations of PET? | Expensive.
Requires specialist facilities and staff.
Relatively low spatial resolution compared to MRI.
Risks need to be managed due to radioactive tracer. |
| What can brain modification be used for? | Brain regions can be permanently removed or brain activity can be temporarily decreased.
Or brain areas can be stimulated to enhance or increase brain activity in that region. |
| How is brain modification relevant to medical treatment? | Psychiatric and neurological conditions are associated with abnormal brain functions. Treatment of these disorders will target the abnormal brain processes involved.
e.g. removal of sections of abnormal brain tissue - epilepsy or brain tumour
Drugs can also be used to selectively target abnormal function of specific neurotransmitter systems. |
| Explain enhancement in the context of brain modification. | 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 unction. |
| How is brain modification relevant to scientific research? | Brain modulation provides information about causation and whether a given brain region is necessary for a particular task.
New techniques to modify specific brain regions or process in living people make it possible to test hypotheses and examine links to behaviour, rather than relying on post-mortem analysis. |
| What are ablation studies? | When a part of the brain is removed to determine its use.
Limited studies. |
| What did Egas Moniz do? | Introduced prefrontal leucotomy for relief of psychiatric disorders.
Frontal lobes linked to personality. |
| What are the personality consequences of frontal leucotomy? | Apathy.
Emotional unresponsiveness.
Disinhibition.
Inability to plan. |
| What is electrical brain stimulation? | Electrodes surgically implanted in specific areas of the brain generate electrical pulses.
Used to reveal precise localisation of cortical function. |
| What is non-invasive electrical brain stimulation (ECT) used for? | Induces seizure.
Used to treat range of mental illnesses, now used to treat severe depression.
Seizures used to reduce psychiatric symptoms.
Mechanism of action unknown.
e.g. transcranial direct current stimulation (tDCS). |
| How does transcranial magnetic stimulation (TMS) work? | A coil carrying an electrical current generates a brief, focal magnetic pulse which activates a small region of cortex underlying the coil.
Activation acts as a "virtual lesion", temporarily disrupting the tissue for a few hundred milliseconds.
Painless process. |
