martes, 11 de junio de 2019

Studying the Human Brain

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By Dr. Ananya Mandal, MDReviewed by Sally Robertson, B.Sc.

The human brain is one of the most complex organs in the human body and damage or disease affecting even the smallest part of the human brain can lead to severe functional impairment. Some techniques that may be used for studying the human brain include:

Electroencephalogram (EEG)

This is a diagnostic test that uses electrodes placed over the scalp to record the electrical activity of the brain, especially the cerebral cortex. The recording of potential differences on the scalp caused by brain activity was first reported by Hans Berger in 1929. This gave rise to the EEG that is used widely today.

The EEG measures mass changes in synaptic activity in the nerves of the brain and is helpful in diagnosing, treating and evaluating diseases that change electrical activity in the brain, such as epilepsy. Around a couple of decades ago, multichannel EEG recording techniques came into use.

These use mathematically extensive modelling algorithms to help locate functional brain areas based on the scalp-potential distributions. This is termed high-resolution EEG.

Magnetoencephalography (MEG)

The first recording of cerebral magnetic fields was performed with an induction coil by David Cohen in 1968. The first recording with a superconducting quantum interference device (SQUID) was also performed by Cohen in 1972. The pioneering research on MEG then began.

MEG can map brain activity by recording the electromagnetic fields that are produced by the naturally occurring electrical currents in the brain. This technique offers a better spatial resolution than EEG and helps to pinpoint problematic sites.

Regional cerebral blood flow imaging has been assessed using radioactive tracer substances since the early 1960s. Such techniques include computed tomography (CT), positron emission tomography (PET) and single photon emission computed tomography (SPECT) scans.

Functional magnetic resonance imaging (fMRI)

Both EEG and MEG have their disadvantages and have been replaced by more recent methods such as functional magnetic resonance imaging (fMRI). This technique can detect the smallest of changes and is useful in both diagnosis of disease and the development of treatments.

fMRI uses very powerful magnets and can localize brain activity changes to regions as small as one cubic millimeter. In addition, it is not an invasive procedure and can be used widely. However fMRI, does fail to provide real-time dynamics of blood flow within the brain.

Photon migration tomography

Photon migration tomography (PMT; also called near-infrared spectroscopy or optical imaging) is another new method for measuring cortical activity and assesses the scattering of near-infrared light from the brain tissue.

Transcranial magnetic stimulation

Transcranial magnetic stimulation is a technique used to excite neurons using strong and time-varying magnetic fields. The procedure is non-invasive and painless.