Just imagine yourselves caught up in a negotiation during an important business meeting, or at the peak of a thrilling poker game, or even on a first date with the person that may become “the one”… Wouldn’t you love to know what the person sitting across from you is thinking? If they are hesitant, scared or excited? What exactly is happening inside their brain?

Brain researchers were always faced with the challenge of cracking the mysteries of the brain. The cardiologist is able to listen to the heartbeat, the orthopedist feels the bone to see if it is broken, and the internist is able to diagnose an enlarged internal organ or an inflamed gland. And what can the neurologist do, since it is not possible to ‘feel’ brain cells that are surrounded by a hard skull?

Long ago, using “skull drillings” to treat mental problems, epilepsy or even strong headaches was common practice. Thankfully for us, medicine and brain research has advanced in leaps and bounds since then, and nowadays researchers and doctors have less invasive methods to diagnose and treat brain-related problems.

Imaging the Brain
The discovery of the X-ray in 1895 revolutionized medical diagnostic capabilities. It seemed that the body became “transparent” at once, and we could easily diagnose things like bone fractures, kidney stones, a bullet that penetrated an internal organ or tooth cavities. X-ray imaging is based upon the differences in densities of different tissues. Bones, for instance, absorb the X-rays better than the soft tissues surrounding them, thus allowing clear recognition of them in the image. In contrast to this, the density of brain tissues is fairly uniform, and therefore it is difficult to recognize specific regions of the brain in a regular x-ray. In addition, these tissues are encapsulated in skull bones, which makes it even more difficult to use x-ray images for diagnosing brain tissue.

All this does not completely exclude the possibility of using an x-ray for observing the brain. In the 1970’s the method of computed tomography (CT) was developed; based on a long series of x-ray images taken at different angles, followed by a computed reconstructed image of the brain. This method allows us to observe the brain in sections as well as receive information regarding structural changes and their impact on various brain functions.

However, medicine has not settled for just structural diagnosis of the brain. The best in the field have worked on developing methods that will enable us to observed real-time brain functions.

Electric Brain
From the very moment that researchers understood that neural activity is executed by electric conduction between the building blocks of the brain i.e.neurons‎, they have sought to find methods to follow this electrical activity and decipher it. In 1924, the German psychiatrist Hans Berger recorded for the first time electrical activity from a human brain. Ever since, this method called electroencephalogram (EEG) became widely used, and is still utilized today for the diagnosis of foci of epileptic attacks, sleep disturbances, coma and as an additional tool for diagnosing brain death.

Another method that is based on the electrical nature of neural activity is MEG – magnetoencephalography. In this method a detector is used to measure the magnetic fields created as a result of the electrical activity. This information is useful for monitoring real-time neural activity at high resolution, as the neurons communicate with one another using electrical currents.

How dare that one photon?
In the imaging method of “single-photon emission computed tomography”, or SPECT in short, a radioactive substance is injected into the subject and it accumulates in certain tissues according to their activity. The radioactive substance decays and emits gamma photons, which penetrate beyond the brain tissue and are received in a special detector that surrounds the head. This makes it possible to collect information from different angles as well as different sections of the brain, using it to create a 3D image of the brain tissue. This method assists with diagnosis of Alzheimer’s disease ‎ and dementia, and also in identification of foci in the brain that cause epileptic attacks.

Thoughts on the scale
During the 19th century, an Italian researcher named Angelo Mosso constructed a device that was designed for measuring the brain during routine activity. According to the original sketches, which are covered in dust in some Italian university’s archive, the device better resembles an ancient torture device rather than the complex brain scanners of our time.

The principle was simple: the brain requires more oxygen when it is active, which increases the blood-flow to it, and therefore it will weigh a little bit more while performing a complicated activity than it did before. Mosso would lay his subjects on a long balanced surface, which served as a scale; with their head at one end and their feet at the other. He then let them listen to sounds that stimulated neural activity and checked how this affected the balance of the surface, as the weight of the brain increased due to blood flow.

Observing brain activity by following blood flow to different parts of the brain is the basis of the modern imaging method fMRI – functional magnetic resonance imaging. In this method, a strong external magnetic field is applied and it influences compounds containing hydrogen, such as water or organic compounds. This method makes it possible, among other things, to detect changes in the hemoglobin that supplies oxygen to the brain. During neural activity, the oxygen consumption increases and the hemoglobin molecules in the brain change according to the amount of oxygen they carry. The fMRI system follows these changes and makes it possible to check which areas of the brain are active during different activities, such as reading, watching a movie, listening to music etc.   

Recently, the New York Times published an article describing an experiment that utilized fMRI, in which subjects were exposed to images and sounds of an iPhone. The subjects presented increased neural activity in areas of the brain associated with emotions. The experiment and its interpretation (a generation infatuated with smartphones) may have been subjected to some criticism, but it does not diminish the advantages of the method, which provides a means to image the brain in different spatial sections and watch real-time neural activity.

As opposed to CT, which is based on ionizing radiation, and SPECT, which is based on radioactive markers, the MRI method is considered safe and free from negative side-effects, aside from the high cost of the system. It is possible to use MRI often and regularly, and use it to scan the brains of healthy subjects for research and monitoring purposes.

MRI machine | Photograph by: Jan Ainali, Wikipedia

What does the future hold?
The most prominent trend in diagnosis and imaging of the brain is the development of methods for locating and directly measuring elements related to brain function. Just a few examples of these types of developments are: markers for neurotransmitters such as dopamine; techniques for detecting changes in the structure of myelin– the material that surrounds neurons and enables neural conductance, as a measurement of brain injury; detection of amyloid-beta-protein clusters that accumulate in the brains of Alzheimer’s patients; and seeking markers that enable the identification of cancer cells.

 

Dr. Anat London
Department of Neurobiology
Weizmann Institute of Science


Article translated from Hebrew by Elee Shimshoni, PhD student at the Weizmann Institute of Science.
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