Neurophysics

Neurophysics (or neurobiophysics) is the branch of biophysics dealing with the development and use of physical methods to gain information about the nervous system. Neurophysics is an interdisciplinary science using physics and combining it with other neurosciences to better understand neural processes. The term "neurophysics" is a portmanteau of "neuron" and "physics". Nanoneurobiophysics is the specialization of neurobiophysics in the nanoscale^[1] as well as a sub-field of nanoscience. Nanoneurobiophysics is focused around the study of demyelinization and neurodegenerative diseases with the final aim to apply the knowledge to the field of nanomedicine (i.e., diagnosing and treating diseases through nanotechnology).^[1]

The methods used include the techniques of experimental biophysics and other physical measurements such as EEG^[2] mostly to study electrical, mechanical or fluidic properties, as well as theoretical and computational approaches.^[3] Among other examples, the theorisation of ectopic action potentials in neurons using a Kramers-Moyal expansion^[4] and the description of physical phenomena measured during an EEG using a dipole approximation^[2] use neurophysics to better understand neural activity.

Otro enfoque teórico bastante distinto considera que las neuronas tienen energías de interacción del modelo de Ising y explora las consecuencias físicas de esto para varias topologías de árboles de Cayley y grandes redes neuronales . En 1981, Peter Barth derivó la solución exacta para el árbol de Cayley cerrado (con bucles) para una relación de ramificación arbitraria ^{[ 5 ]} y encontró que exhibía un comportamiento de transición de fase inusual ^{[ 6 ]} en sus correlaciones locales de ápice y de sitio a sitio de largo alcance, lo que sugiere que la aparición de fenómenos cooperativos determinados estructuralmente e influenciados por la conectividad puede jugar un papel significativo en grandes redes neuronales.

Las técnicas antiguas para registrar la actividad cerebral mediante fenómenos físicos ya están muy extendidas en la investigación y la medicina . La electroencefalografía (EEG) utiliza la electrofisiología para medir la actividad eléctrica dentro del cerebro. Esta técnica, con la que Hans Berger registró por primera vez la actividad eléctrica cerebral en un ser humano en 1924, ^{[ 7 ]} no es invasiva y utiliza electrodos colocados en el cuero cabelludo del paciente para registrar la actividad cerebral. Basándose en el mismo principio, la electrocorticografía (ECoG) requiere una craneotomía para registrar la actividad eléctrica directamente en la corteza cerebral .

In the recent decades, physicists have come up with technologies and devices to image the brain and its activity. The Functional Magnetic Resonance Imaging (fMRI) technique, discovered by Seiji Ogawa in 1990,^[8] reveals blood flow changes inside the brain. Based on the existing medical imaging technique Magnetic 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, the Two Photons Microscopy (2P), invented by Winfried Denk (for which he has been awarded the Brain Prize in 2015^[9]), John H. Strickler and Watt W. Webb in 1990 at Cornell University,^[10] uses fluorescent proteins and dyes to image brain cells. This technique combines the two-photon absorption, first theorized by Maria Goeppert-Mayer in 1931, with lasers. Today, this technique is widely used in research and often coupled with genetic engineering to study the behavior of a specific type of neuron.

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 cerebral electromagnetic field generated by the action potentials triggered during brain activity.^[11] These theories are called electromagnetic theories of consciousness. Another group of hypotheses suggest that consciousness cannot be explained by classical dynamics but with quantum mechanics and its phenomena. These hypotheses are grouped into the idea of quantum mind^[12] and were first introduced by Eugene Wigner.

Among the list of prizes that reward neurophysicists for their contribution to neurology and related fields, the most notable one is the Brain Prize, whose last laureates are Adrian Bird and Huda Zoghbi for "their groundbreaking work to map and understand epigenetic regulation of the brain and for identifying the gene that causes Rett syndrome".^[13] The other most relevant prizes that can be awarded to a neurophysicist are: the NAS Award in the Neurosciences, the Kavli Prize and to some extent the Nobel 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 as Neher and Sakmann in 1991 for the patch clamp, and also to Lauterbur and Mansfield for their work on Magnetic resonance imaging (MRI) in 2003.

• Wulfram Gerstner and Werner M. Kistler, Spiking Neuron Models, Single Neurons, Populations, Plasticity, Cambridge University Press (2002)Archived 2019-03-24 at the Wayback MachineISBN 0-521-89079-9ISBN 0-521-81384-0
• Alwyn Scott, Neuroscience: A Mathematical Primer, Birkhäuser (2002)ISBN 0-387-95403-1
• Graben, Peter; Zhou, Changsong; Thiel, Marco; Kurths, Jürgen (2008), "Foundations of Neurophysics", Lectures in Supercomputational Neurosciences, Berlin, Heidelberg: Springer, pp. 3–48, Bibcode:2008lsn..book.....G, doi:10.1007/978-3-540-73159-7, ISBN 978-3-540-73159-7