Neurophysics (orneurobiophysics) is the branch ofbiophysics dealing with the development and use of physical methods to gain information about thenervous system. Neurophysics is an interdisciplinary science using physics and combining it with otherneurosciences to better understand neural processes.The methods used include thetechniques of experimental biophysics and other physical measurements such asEEG[1] mostly to studyelectrical,mechanical orfluidic properties, as well astheoretical and computational approaches.[2] The term "neurophysics" is aportmanteau of "neuron" and "physics".
Among other examples, the theorisation of ectopicaction potentials in neurons using aKramers-Moyal expansion[3] and the description of physical phenomena measured during an EEG using a dipole approximation[1] use neurophysics to better understand neural activity.
Another quite distinct theoretical approach considers neurons as havingIsing model energies of interaction and explores the physical consequences of this for variousCayley tree topologies and large neural networks. In 1981, the exact solution for the closed Cayley tree (with loops) was derived byPeter Barth for an arbitrary branching ratio[4] and found to exhibit an unusualphase transition behavior[5] in its local-apex and long-range site-site correlations, suggesting that theemergence of structurally-determined and connectivity-influenced cooperative phenomena may play a significant role in large neural networks.
Old techniques to record brain activity using physical phenomena are already widespread inresearch andmedicine.Electroencephalography (EEG) useselectrophysiology to measure electrical activity within the brain. This technique, with whichHans Berger first recorded brain electrical activity on a human in 1924,[6] is non-invasive and uses electrodes placed on the scalp of the patient to record brain activity. Based on the same principle,electrocorticography (ECoG) requires acraniotomy to record electrical activity directly on thecerebral cortex.
In the recent decades, physicists have come up with technologies and devices to image the brain and its activity. TheFunctional Magnetic Resonance Imaging (fMRI) technique, discovered bySeiji Ogawa in 1990,[7] reveals blood flow changes inside the brain. Based on the existing medical imaging techniqueMagnetic Resonance Imaging (MRI) and on the link between the neural activity and the cerebral blood flow, this tool enables scientists to study brain activities when they are triggered by a controlled stimulation. Another technique, theTwo Photons Microscopy (2P), invented byWinfried Denk (for which he has been awarded theBrain Prize in 2015[8]), John H. Strickler andWatt W. Webb in 1990 atCornell University,[9] usesfluorescent proteins and dyes to imagebrain cells. This technique combines the two-photon absorption, first theorized byMaria Goeppert-Mayer in 1931, with lasers. Today, this technique is widely used in research and often coupled withgenetic engineering to study the behavior of a specific type ofneuron.
Consciousness is still an unknown mechanism and theorists have yet to come up with physical hypotheses explaining its mechanisms. Some theories rely on the idea that consciousness could be explained by the disturbances in the cerebralelectromagnetic field generated by theaction potentials triggered during brain activity.[10] These theories are calledelectromagnetic theories of consciousness. Another group of hypotheses suggest that consciousness cannot be explained byclassical dynamics but withquantum mechanics and its phenomena. These hypotheses are grouped into the idea ofquantum mind[11] and were first introduced byEugene Wigner.
Among the list of prizes that reward neurophysicists for their contribution to neurology and related fields, the most notable one is theBrain Prize, whose last laureates areAdrian Bird andHuda Zoghbi for "their groundbreaking work to map and understand epigenetic regulation of the brain and for identifying the gene that causes Rett syndrome".[12] The other most relevant prizes that can be awarded to a neurophysicist are: theNAS Award in the Neurosciences, theKavli Prize and to some extent theNobel Prize in Physiology or Medicine. It can be noted that a Nobel Prize was awarded to scientists that developed techniques which contributed widely to a better understanding of the nervous system, such asNeher andSakmann in 1991 for thepatch clamp, and also toLauterbur andMansfield for their work onMagnetic resonance imaging (MRI) in 2003.
