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Brain Research Methods

Transcranial Magnetic Stimulation (TMS) Positron Emission Tomography (PET)

Hayley Nancarrow

on 23 May 2011

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Transcript of Brain Research Methods

Brain Research Methods Transcranial Magnetic Stimulation (TMS) Positron Emission Tomography (PET) Introduction:
Transcranial Magnetic Stimulation (TMS) is a relatively recent technique for both the treatment of cognitive disorders such as depression or auditory hallucinations, and for brain research. It is a type of direct brain stimulation in which, a magnetic field pulse is used to pentrate the skull and temporarily affects the brain activity. The magnet either temporarily activates, or disrupts the normal activity of the neurons in a specific area of the cerebral cortex. It only effects the brain to a depth of 2-3 centremetres and no other area of the brain is affected other than those that are underneath the magnetic copper coil. How it works? TMS involves a handheld device being held or controlled and manouvered around to specific areas of the head. The magnetic field induces a harmless electrical current in a series of time varying pulses. While this happens the patient, is fully awake and alert. TMS is a good method because it is non-invasive and does not involve admistration of any substances or anaesthetic. There are two types of TMS; repetitive TMS and non-repetitive TMS. Repetitive TMS Non-Repetitive TMS Repetitive TMS involves a procedure using repeated, but not always rapid, delivery of magnetic pulses. Non-repetitive TMS involves a procedure of delivering single magnetic pulses. Benefits of TMS and what it is useful for :) TMS is useful for determing which brain areas are responsible for which behaviours.
It can simulate what happens when the brain is damaged. Allows ethical brain research, with very minimal side effects.
It can also be used for diagnostic purposes. To assess cortical brain damage, and to track patient recovery. Limitations of TMS In some cases, patients have reported experiencing headaches after treatment.
It can only penetrate to a very shallow layer of the brain. Tends to not be as exact as direct brain stimulation.
Patients tend to not return to this type of testing, due to the headaches and seizures that have been reported. Case Studies In an experiment undertaken by the Department of Otolaryngology-Head and Neck Surgery, University of Arkansas for Medical Sciences, it was hypothesised that improvements of tinnitus would be experienced, after low frequency TMS. Positron emission tomography and computed tomography imaging (PET-CT) alongside TMS was performed on a 43-year-old white male with more than a 30 year history of bilateral tinnitus (loud sounds in the ears, and constant ringing). rTMS was administered to the area in the brain of increased cortical activation visualized on PET-CTscan. This was continued for 5 days. The results showed that the most marked reduction in tinnitus severity occurred after rTMS treatment; this continued up to 4 weeks after rTMS. This concluded that, Low-frequency rTMS applied to the primary auditory cortex can reduce tinnitus severity. This method allows researchers to assess and discover how cognitive functions relate to our human behaviour. The method has many potential benefits as TMS can be used clinically to measure activity and function of specific brain circuits in humans. The most strongest and widely-accepted use is in measuring the connection between the primary motor cortex and a muscle to evaluate damage from strokes, spinal cord injuries, multiple sclerosis and motor neuron disease. TMS has been suggested as a means of assessing short-interval intracortical inhibition (SICI) which measures the internal pathways of the motor cortex but this use has not yet been validated. Positron Emission Tomography or PET scan as
it is commonly called, is a test that uses a special type of camera and a tracer (radioactive chemical) to look at organs in the body and is used in brain research. It provides information about the functioning
of various parts of the brain. It can be combined with
CT scans to exam other parts of the body to assess different
diseases and conditions. Prior to the scan being taken the patient is given a
sugar-like substance that contains radioactive
elements. When the substance enters the bloodstream
it travels to the brain and has the ability to highlight regions
that have minimised glucose and oxygen. With the assisstance of cognitive activities such as remembering, thinking, imagining talking, or moving;
different areas of the brain are stimulated, and the substance emits bright colours on the display of the PET scanner. Case Study --> Alzheimer's Disease - FDG PET in Alzheimer’s Disease

Clinical History
A 64 year old male patient presented with subacute disorientation and problems with speech. There was no other relevant clinical history, family history, or prior conditions, except for obesity. The patient's current symptoms included neglect and disorientation. The patient was hospitalized after he ran away and was unable to find his way back home.

Indication for FDG PET:
A PET scan was ordered to investigate any additional underlying neurodegenerative patterns.

Imaging Findings Limitations Because the doses of radioactive tracer administered are small, diagnostic medicine procedures like this one result in low radiation exposure. This isnt harmful, although continuous exposure over time could harm the patient.
Due to the need for a radioactive substance, the PET session must be kept short so that the person does not recieve too much radiation.
Can have difficulty in picking up rapid progression or changes in brain activity associated with brain function.
The resolution of structures of the brain with PET scan may not be as clear as with other imaging techniques, such as CT or MRI. PET was originally designed to diagnose
abnormalities in the brain and is highly
effective if the area under view is structurally
sound. It can also provide information on the brain
function of specific groups or populations of research
interest such as people with mental illnesses. FDG PET Findings
The FDG PET scan revealed a clear bilateral reduction of glucose metabolism in the temporoparietal and frontal lobes. The subcortical structures, motor cortex, visual cortex and the cerebellum showed normal glucose uptake.

The findings of the PET scan were strongly suggestive of Alzheimer's disease. Due to the normal glucose metabolism of the subcortical structures, as well as the primary cortical areas such as motor cortex and visual cortex, Lewy body disease is rather unlikely.

Data courtesy of Koen Van Laere, M.D., Ph.D., Dr. Sc., Leuven University Hospital, Belgium.
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