Methods

Repetitive Transcranial Magnetic Stimulation (rTMS)

rTMS delivers repeated short electromagnetic pulses through a coil magnetic to a specific site in the brain. Magnetic pulse passes through skull, and causes small electrical currents that stimulate nerve cells in the targeted brain region. Can inhibit brain function. For example rTMS can be applied over the Broca's area temporarily blocking out ones ability to speak. This functional knockout aspect of rTMS is currently the focus of intense research into language (speech production).

Positron Emission Tomography (PET)

type of nuclear medicine imaging. Shows how organs and tissues are working. Different than magnetic resonance imaging (MRI) and computed tomography(CT), which show the structure of and blood flow to and from organs. A radioactively labelled compound called a "radioisotope" is injected into a vein and travels through the blood and collects in organs and tissues. For example: if glucose is loaded with a radioisotope then brain metabolism can be monitors. Radioisotope have a short-half life: it loses its radioactivity within minutes or hours. When a radioisotope decays it emits a positron. Positrons collide with electrons, annihilating each other and emitting two gamma rays.

sMRI: How it works?

- An MRI scanner produces an intense magnetic field. - Like compass needles, the protons align themselves with the magnetic field, but still spin around their axis. - As they spin the proton "wobbles". The stronger the field, the greater the frequency of wobble (or "rocking"). - The scanner produces a radio signal that knocks the protons out of alignment and gives them more energy. - Protons promptly realign and release the extra energy, which is detected by the scanner. - Computers translate these signals to produce the image.

Disadvantages of EEG

- EEG does not measure activity at subcortical levels, as a result, EEGs do not provide a very clear picture of the structure of the brain. - Poor spatial resolution, not like fMRI which can directly display areas of the brain which are active. - Cannot identify specific locations in the brain at which various neurotransmitters, drugs, etc. can be found. - Time consuming to connect electrodes to scalp.

Types of Brainwaves

- Gamma brainwaves fastest of brain waves, relate to simultaneous processing of information from different brain areas. Pass information rapidly, and as the most subtle of the brainwave frequencies. - Beta brainwaves dominate normal waking state of consciousness when attention is directed towards cognitive tasks and the outside world. Beta is a 'fast' activity, present when we are alert, attentive, engaged in problem solving, judgment, decision making, and engaged in focused mental activity. - Alpha brainwaves are present during quietly flowing thoughts, but not quite meditation. Alpha waves aid overall mental coordination, calmness, alertness, mind/body integration and learning. - Theta brainwaves occur most often in sleep, also dominant in deep meditation. Acts as our gateway to learning and memory. It is that twilight state which we normally only experience fleetingly as we wake or drift off to sleep. - Delta brainwaves are the slowest but loudest brainwaves. Generated in deepest meditation and dreamless sleep. Healing and regeneration are stimulated in this state, this is why deep restorative sleep is so essential to the healing process.

Electroencephalogram (EEG)

Records changes in brainwaves . A wave is any type of brain activity, which appears as a 'wave' shape on the EEG recording. EEG records electrical activity produced by the brain's neurons through the use of electrodes that are placed around the head. Can detect if a person is asleep, awake, or anesthetized because the brain wave patterns are known to differ during each state. Tracks brain waves that are produced when a person is reading, writing, and speaking, and are useful for understanding brain abnormalities, such as epilepsy. A particular advantage of EEG is that the participant can move around while the recordings are being taken, which is useful when measuring brain activity in children who often have difficulty keeping still. By following electrical impulses across the surface of the brain, researchers can observe changes over very fast time periods.

Summary

- Measures of electrical activity in the brain, such as electroencephalography EEG are used to assess brain-wave patterns and activity. - MEG is a non-invasive neurophysiological technique that measures the magnetic fields generated by neuronal activity (measure structure). - CAT and MRI are used to measure brain function fMRI measures blood flow in the brain during different activities, providing information about the activity of neurons and thus the functions of brain regions. - fMRI gold standard of imaging techniques. - Transcranial magnetic stimulation (TMS) is a non invasive technique used to temporarily and safely deactivate a small brain region, with the goal of testing the causal effects of the deactivation on behaviour. - DBS is an invasive treatment, requires implantation of a brain pacemaker which sends electrical impulses, through implanted electrodes, to specific parts of the brain.

TMS: How it works?

- Patients are first scanned in an fMRI machine to determine exact location of area of brain to be tested. - TMS works by placing a coil close to the scalp. - The coil emits a powerful magnetic field that easily penetrates through skin and bone. - Electrical stimulation is provided to the brain before or while the participant is working on a cognitive task, and the effects of the stimulation on performance are assessed. - If the persons ability to perform the task is influenced by the presence of the stimulation, then the researchers can conclude that this particular area of the brain is important to carrying out the task.

EEG: How does it work

- Populations of neurons generate electromagnetic fields when they are active - This electrical activity can be measured on the scalp - EEG directly measures neuronal activity it has fantastic resolution (milliseconds) - Spatial resolution is poor - Recorded by electrons secured to the scalp - One electrode is the reference and is placed on an inactive site (e.g behind the ear) - Electrodes record the dendritic currents (post synaptic potentials) and action potentials associated with 1000's of neurons as well as artifacts (e.g muscle, eye movements) - These measurements take the form of a wave: millivolts (mV), as a function of time - The waveforms representing the electrical potential have a characteristic frequency and size (i.e, mV) depending upon the state of the individual - Brainwaves change according to what we're doing and feeling. - Slower brainwaves are dominant we can feel tired, slow, sluggish, or dreamy. The higher frequencies are dominant when we feel wired, or hyper-alert.

PET: How it works?

- Radioisotopes are injected, and begin to decay. - Active brain regions demand more oxygen and glucose. - Oxygen and glucose accumulate in these regions. - When radioisotopes spontaneously decay they emit a positron. - Positrons collide with electron: two gamma rays travelling in opposite direction produced. - PET scanner consists of a donut ring lined with detectors. Detectors sensitive to gamma rays. - Computers construct a picture of brain activity. CAT scans can work as an early warning system for the subsequent development of Alzheimer's disease.

sMRI: How is the image produced?

- The computer calculates the density of hydrogen atoms found in a single cross section. - Hydrogen density reflects water content. - Different types of tissue contain different concentrations of water. - Computer algorithms determine tissue type. - sMRI is safe and gives superior spatial resolution to that of either CT scans or photographs of dissections. - But no injections, no needles, and no phobias.

fMRI: How it works?

- The patient lies on a bed within a large cylindrical structure containing a very strong magnet. - Neurons that are firing use more oxygen, and the need for oxygen increases blood flow to the area. - The fMRI detects the amount of blood flow in each brain region, and thus is an indicator of neural activity. - Very clear and detailed pictures of brain structures are produced - Images take the form of cross-sectional "slices" that are obtained as the magnetic field is passed across the brain - The images of these slices are taken repeatedly and are superimposed on images of the brain structure itself to show how activity changes in different brain structures over time. - The patient is asked to engage in tasks while in the scanner (e.g., by playing a game with another person), the images can show which parts of the brain are associated with which types of tasks. Advantages: Combines structural and functional data on the same image. Produces three-dimensional images of the whole brain activity. Greater spatial resolution compared to PET. No injections, no needles, no phobias.

5 reasons to be skeptical

1. Unnatural environment for cognition. It's hard to stay relaxed and focused inside a narrow tube filled with a loud thumping sound. 2. Scans are not direct measures of brain activity. The fMRI machines measure proton alignment and density, not neural activity and not in real time. 3. The coloured indicators are misleading. What appears to be a highly localised process may in fact be distributed right across the brain. 4. Brain images are statistical averages. Data are pooled within or between subjects (usually small samples), but where are the error statistics! 5. Brain areas activate for different reasons. Just because your amygdala lights up, doesn't mean you're feeling fear. For example, the cingulate gyrus has been identified as the home of over 57 tasks. More likely parts of the brain are members of a neural network, andthat processing is diffuse. Images Are Not the Evidence in Neuroimaging.

Computed Axial Tomography (CAT) Scanners

CAT scan is a sophisticated x-ray of the brain. Tomography is the process of generating a 2-dimensional image of a slice or section through a 3-dimensional object. The CT scanner uses digital geometry processing to generate a 3-dimensional (3D) image of the inside of the brain. The 3D image is made after many 2-dimensional (2D) X-ray images are taken around a single axis of rotation. Typically, in one 360 rotation, about 1,000 profiles are sampled. Each profile is subdivided spatially (divided into partitions) by the detectors and fed into about 700 individual channels. Each profile is then backwards reconstructed (or "back projected") by a dedicated computer into a two-dimensional image of the "slice" that was scanned. Advantages: Permits highly accurate data on specific regions of brain injury which can be correlated to brain function. Non invasive and painless. Safe, accurate, and affords rapid diagnosis of brain damage (e.g. tumours, cysts or injuries). Disadvantages: Exposure to radiation. Allergic reaction to contrast Not suitable to pregnant women or young children.

Deep Brain Stimulation (DBS )

First developed as a treatment for Parkinson's disease to reduce tremor, stiffness, walking problems and uncontrollable movements. Invasive treatment, requires neurosurgery. Implantation of a medical device called a brain pacemaker which sends electrical impulses, through implanted electrodes, to specific parts of the brain patients are awake during the procedure. DBS leads are placed in the brain according to the type of symptoms to be addressed. For example: non-Parkinsonian essential tremor the lead is placed in the ventrointermediate nucleus (VIM) of the thalamus for dystonia and symptoms associated with Parkinson's disease (rigidity, bradykinesia and tremor), OCD and Depression to the nucleus Accumbens.

DBS and Obsessive Compulsive Disorder

In the case of OCD, the electrodes are placed in a different part of the brain believed to be associated with the disorder. Although it is unclear exactly how the device works to reduce depression or OCD, scientists believe that the pulses help to "reset" the area of the brain that is malfunctioning so that it works normally again.

Magnetic Resonance Imaging (MRI)

MRI gives us the most detailed picture of the brain the patient is positioned within an MRI scanner which forms a strong magnetic field around the area to be imaged the magnetic field temporarily realigns hydrogen atoms in your brain. Radio waves cause these aligned atoms to produce very faint signals which are used to create cross-sectional MRI images. MRI is widely used in hospitals for medical diagnosis, staging of disease and for follow-up without exposure to radiation.

X-Rays: Cerebral Angiography

Minimally invasive x-ray, procedure to detect or confirm abnormalities within the blood vessels in the brain. Which uses an iodine-containing contrast material to produce pictures of blood vessels in the brain. Catheter inserted into an artery in the leg or arm through a small incision in the skin and threaded through the circulatory system to the carotid. Contrast material is injected through the catheter and images are captured using ionizing radiation (x-rays). Useful for visualising the cerebral vascular system and detecting vascular damage.

Diffusion Tensor Imaging (DTI)

Network Connectivity refers to interaction between neural areas in carrying any specific function. Diffusion tensor imaging (DTI) uses MRI to trace white matter tracts and the diffusion of water molecules in particular directions due to the presence of myelinated fibers. Measures both the degree and direction of water diffusion. Can reveal the degree of structural integrity of white matter. Widely used in stroke and Traumatic Brain Injury.

X-Rays

Non invasive. Different tissue types absorb different amounts of X-ray energy. Denser tissue absorbs (attenuates) more. X-ray beam is passed through the body onto a photographic screen. The level of an X-ray exiting the body depends on the tissue it has travelled through. Effective only if the difference between structures in absorbing X-rays is substantial. Not useful for visualising the brain.

Transcranial Magnetic Stimulation (TMS)

TMS is a procedure in which brief and intense single magnetic pulses are applied to the brain of living persons with the goal of temporarily activating or deactivating a specific area of the brain. The TMS magnetic field interacts with resting neurons and induces small electrical currents to flow in them. However, the device can only stimulate neurons close to the surface of the cortex as its maximum range is only 2-3 cm, because field strength drops off rapidly with distance. TMS can interfere with some of the brains basic functions thus mimicking brain lesions, but only for a short time. A single pulse to the motor cortex may for example cause a limb to move. A single pulse to the visual cortex can generate a flash of light.

DBS and Parkinson's Disease

Used for patients whose symptoms cannot be controlled by medication. Is not a cure, but can mitigate symptoms such as tremors, rigidity and bradykinesia. Targets specific areas of brain related to Parkinson's, subthalamic nucleus (STN) and the globus pallidus interna (GPi).

Functional MRI (fMRI)

a combination of the PET scan and the MRI. fMRI can give us the best picture of the brain while showing use blood flow information. Detects changes in blood oxygenation and flow that occur in response to neural activity. When a brain area is more active it consumes more oxygen. To meet this increased demand blood flow increases to the active area. fMRI can be used to produce activation maps showing which parts of the brain are involved in a particular mental process.

Magnetoencephalography (MEG)

a non-invasive neurophysiological technique that measures the magnetic fields generated by neuronal activity of the brain Magnetic fields are detected by a sophisticated technology based on super-conducting detectors and amplifiers (SQUIDS). Spatial distributions of the magnetic fields are analysed to localize the neuronal sources of the activity within the brain locations of the sources are superimposed on anatomical images, such as MRI, to provide information about both the structure and function of the brain MEG combines excellent spatial and temporal resolution to provide the unique opportunity to characterize the spatiotemporal properties of cortical activation associated with sensory and cognitive function. Principles: Electrical activity in neurons produces magnetic fields that can be recorded outside the skull and used to calculate the locations of the activity within the brain. Properties: MEG has the advantages of very high temporal and spatial resolution, however it requires highly sensitive instrumentation and sophisticated methods for eliminating environmental magnetic interference.

Structural Magnetic Resonance Imaging (sMRI)

non-invasive technique for examining the physical structure of the brain (anatomy). Information from sMRI can be used to describe the shape, size, and integrity of grey and white matter structures in the brain. Many sMRI scan sequences are volumetric, meaning that measurements can be made of specific brain structures to calculate volumes of tissue.