Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_123_библиотеки_им_акад_М_И_Перельмана
.pdf
CHAPTER 20 Ten Technologies Revolutionizing BrainScience 371
Chapter20
Ten Technologies
Revolutionizing
BrainScience
R
evolutions are occurring today in neurobiology. Genetic techniques permit
researchers to sequence genomes, visualize gene expression, and modify
genes in the nervous system. With new imaging methodologies, researchers
can monitor neuronal activity electrically, optically, and chemically within single
cells and in the living brain. Brain-computer interfaces show great promise in
restoring function in nervous system injuries and disorders.
Together with traditional funding agencies, new government-backed and non-
prot neuroscience initiatives are developing innovative tools and techniques to
understand how the brain controls behavior and what happens in brain
dysfunction.
This chapter briey highlights ten important technologies developed in the quest
to understand how the brain works.
IN THIS CHAPTER
»
Checking out amazing advances in
neurobiology
»
Knowing what might be possible in
the future of neurobiology
https://t.me/med1917
372 PART 4 The Part of Tens
Cultured Slices, Cells,and Organoids
Cultured mammalian brain slices and cells are providing insights into neural
function. Brain slices can be maintained in culture for hours to days. Neuronal and
glial cells can be isolated from brain tissue or grown from embryonic stem (ES)
cells and studied in culture for weeks to months.
Cultured slices and cells are accessible for electrophysiology, drug testing, and
genetic studies. They’re ecient and economical and lessen the need to use as
many laboratory animals in experimental testing.
One culture technique is to transform adult somatic cells to induced pluripotent
stem (iPS) cells. iPS cells can then be dierentiated to neurons and glial cells in
culture. iPS cells can be generated from patients with genetically based or idio-
pathic disorders to study isolated, generated tissue that may be aected in or
underlie these disorders.
Dierentiated iPS cells can be investigated using electrophysiology, microscopy,
and neurogenetics. They can be used to test pharmacological and genetic thera-
pies and as a cell populations for transplantation, such as replacing dopaminergic
neurons in patients with Parkinson’s disease.
Progress has been made in constructing tissues that can restore organ function.
Cultures of neural cell aggregates are called neural organoids. They’re being used to
investigate brain development, disease progression, and drug eects. Neural
organoids may provide experimental preparations for modeling brain disorders,
discovering new drugs and gene therapies, and as surrogate brain tissues for
transplantation.
Fluorescence, Confocal, and
Two-Photon Microscopy
To understand the structure of the nervous system and how it works, being able
to see it is valuable. Here are a few techniques that neurobiologists use:
»
Fluorescence microscopy: This is used to image structures in xed or live
tissues or cells, and intact animals. It works by using light to excite either an
articial uorescent dye put into the cells or by manipulating the cell to
synthesize a uorescent reporter protein.
https://t.me/med1917
CHAPTER 20 Ten Technologies Revolutionizing BrainScience 373
»
Single photon confocal imaging: Confocal imaging increases contrast and
resolution by using a laser to excite uorescent dyes across one narrow depth
level of tissue at a time. A series of two-dimensional images can be assembled
into three-dimensional images. Using dierent uorescent probes that emit at
dierent wavelengths, researchers can measure several signals concurrently.
»
Two-photon microscopy: This technique uses laser light in the infrared range
so that two photons are simultaneously absorbed by the reporter. The
reporter then uoresces as though it had absorbed a single higher-energy
photon. It has better spatial resolution and less photodamage of the tissue.
Spatial resolution can be improved in super-resolution microscopy by
changing the timing, angle, and patterns of the lasers.
These techniques can image and resolve single synapses. Other applications
include imaging calcium signals, membrane potentials, neurotransmitter levels,
or neuronal activity levels invivo. In photo-pharmacology, chemicals such as glu-
tamate are released from an inactive form by the uorescent light.
Advances in Electrical Recordings
Extracellular electrodes can be used for single or multiple unit recordings, whole
nerve recordings, and eld potentials. Recordings reveal the ring patterns of
neural responses during behavior or in response to stimuli. Extracellular record-
ings can be very stable, lasting for days or months.
Intracellular recordings using sharp or patch electrodes study inputs to and
behavior of single neurons (refer to Chapter4):
»
A sharp electrode is a glass micropipette with a very small tip, enclosing a wire
and conductive salt solution. The electrode is inserted inside the neuron, and
changes in the membrane potential and currents can be monitored for
several hours.
»
A patch electrode has a larger tip that is placed against the cell membrane,
where a seal is made by suction. The larger tips of patch pipettes make
injecting current, dyes, or protein modulators into cells more practical.
Patch pipette recording has revolutionized the understanding of single
neuron electrical properties and activities. It can provide information on how
pharmaceuticals, DNA-based alterations, or experimenter-induced activity
patterns can aect specic neuronal activities or channels.
https://t.me/med1917
374 PART 4 The Part of Tens
Neurogenetics
Neurogenetics is a eld of neurobiology that focuses on understanding the contri-
bution of genetics to the function and dysfunction of the nervous system. Here we
describe neurogenetic techniques for genome sequencing and measuring gene
expression (refer to Chapter2).
Genome sequencing
The global Human Genome Project was a breakthrough that used rst generation
sequencing. Today next generation sequencing (NGS) techniques have increased
eciencies with more applications. Techniques for DNA sequencing (DNA-Seq)
are specic to the genome while RNA sequencing (RNA-Seq) is for sequencing
RNAs, gene expression, and the transcriptome.
Only a small percentage of genomic DNA encodes RNAs and proteins, called
exomes. Exosomes are typically the regions of DNA responsible for genetic disor-
ders. Whole exome sequencing is rapid and aordable.
Genome-wide association study (GWAS) is a powerful technique for identifying
gene variations that contribute to susceptibility to developing neurological
diseases and mental disorders. GWAS has identied risk genes in Alzheimer’s,
Parkinson’s, and Huntington’s disease, multiple sclerosis, autism spectrum
disorder, depression, and schizophrenia.
Gene expression
Epigenetics involves modication of DNA and histones (without changing the DNA
sequences) that contribute to control of gene expression. Researchers are investi-
gating the disruption of epigenetic regulators and modications as contributors to
neurological diseases and mental disorders.
Traditional techniques to measure gene expression involve northern blots, quan-
titative PCR, in situ hybridization, and microarrays (gene chips). Today, variations
of RNA-Seq are being used to measure gene expression in populations of cells and
in individual neurons or glial cells.
https://t.me/med1917
CHAPTER 20 Ten Technologies Revolutionizing BrainScience 375
Genetic Manipulation of Neural Cells
Genetically manipulated animals have provided models to study neurodevelop-
mental, neurological, and psychiatric disorders. Recent gene editing technologies
makes the generation of animal models and manipulation of genes more specic
and accessible.
In knock-out animals, a gene or its part is deleted in the genome to diminish its
protein expression. Conditional knock-outs use promotors that provide control of
the timing and location of the genetic changes. Genetic knock-ins substitute a
genetic abnormality for a normal gene.
Genetic abnormalities can potentially be treated using gene therapies. DNA and
RNA viruses are engineered with sequences that knock out defective host genes or
insert new genes into the host to correct for the genetic abnormality.
The microbial defense system CRISPR/Cas9 is a gene-editing technology. It has
been used for manipulation of genes, to engineer animal models of neurological
disorders, to test gene therapies, and to study large-scale functional genomics in
neural cells. Gene editing holds great promise for genetic treatments of neuro-
logical and mental disorders.
Brain Imaging: Optical, Magnetic,
and Electrical
Until the 1970s, the only widely used techniques to study activity or structure in
the intact brain were single-cell recordings, electroencephalography (EEG) and
X-rays/CT scans.
Today more powerful techniques monitor brain structure and function, including
the following:
»
Optical recording: Optical reporting techniques use uorescent reporter
dyes that change their uorescence in response to voltage or ion concentra-
tions changes in neurons. These dyes allow neurobiologists to record neural
activity using a microscope-linked camera from individual or groups of cells
invivo or in tissue slices.
»
Magnetic resonance imaging (MRI): Certain molecules in the body, when
placed in a strong magnetic eld, align along the eld. Sending radio waves
into the tissue tilt the alignment. When the radio waves are turned o, the
https://t.me/med1917
376 PART 4 The Part of Tens
atoms then return to the original (magnetically induced) alignment. As they
return, they emit an electrical signal that’s captured by a receiver, processed
by a computer, and converted into an image of the brain with millimeter
resolution.
»
Functional MRI (fMRI): This technique uses changes in the amount of
hemoglobin in a given brain area (blood ow) or its amount of oxygenation
(blood oxygen level dependent) to give an index of brain activity in a particular
area, with centimeter resolution.
»
Magnetic encephalography (MEG): MEG measures the small magnetic
elds associated with current ow in the brain. It has moderately high spatial
resolution, approaching fMRI, with simultaneously high temporal resolution
like EEG.
Electrical Brain Stimulation
An advantage of using electrical stimulation to modify human brain activity is it
reduces the side eects that can occur with pharmacological treatments. It’s also
rapid, easily and immediately modiable, and reversible. Here are some of the
recent techniques used in brain stimulation.
Transcranial magnetic stimulation
Transcranial magnetic stimulation (TMS) involves a short-duration high mag-
netic eld pulse via a coil outside the head over the brain area to be stimulated.
This produces relatively localized, transient electrical currents that stimulate or
disrupt neural activity. TMS has been used to treat depression, posttraumatic
stress disorder, epilepsy, and migraines, by stimulating specic brain areas (refer
to Chapters4 and18).
Transcranial direct current stimulation
Transcranial direct current stimulation (tDCS) involves passing a small direct
current between two electrodes on the scalp. Brain regions near the anode gener-
ally appear to be stimulated, whereas areas near the cathode may be inhibited.
Small electrical currents may increase neural spontaneous activity or enhance
signal-to-noise ratios.
https://t.me/med1917
CHAPTER 20 Ten Technologies Revolutionizing BrainScience 377
Long-lasting improvements in learning or cognitive performance from tDCS have
been reported— from improving math performance to alleviating symptoms in
schizophrenia to enhancing cognitive function in the elderly. tDCS may prove to
be a valuable tool for modulation of brain activity.
Deep brain stimulation
Deep brain stimulation (DBS) involves implanting tiny electrodes within particu-
lar brain regions to deliver electrical currents to alter brain activity (refer to
Chapter12). Clinicians have successfully used DBS to treat Parkinson’s disease by
stimulating areas to compensate for the dopamine decit. Clinicians have also
used DBS to treat individuals with chronic pain, treatment resistant depression or
epilepsy (see the section “Brains Interfaced with Computers” later in this chapter).
Optogenetics
Electricity can stimulate networks of neurons but isn’t ideal for precise control of
specic neural activity within the circuit. Optogenetics is used to precisely control
neuronal activity by activating light-sensitive channels that are articially
expressed in the membranes of particular neurons. Researchers have cloned these
channels from microbes that evolved them to control specic behaviors, such as
moving toward light. The channel genes are introduced into and expressed in the
neurons. Applying a light stimulus to the brain area then activates or inhibits only
those neurons that express the microbial light channels. The neuronal response to
the light depends on the optogenetic channel’s properties.
Optogenetics allows scientists to monitor and modulate activity of individual neu-
rons in freely moving animals. Development of cell-specic promoters and
micro-optical stimulators is ongoing to target specic neurons. Optogenetics has
the potential to advance the basic understanding of neural circuit operation and
oer insights into neurological dysfunctions.
Microelectrode Arrays
Scientists developed microelectrode arrays (also called multielectrode arrays) to
explore neural circuit operation and stimulate small numbers of neurons to con-
trol specic circuits.
https://t.me/med1917
378 PART 4 The Part of Tens
Microelectrode arrays contain from tens to thousands of extracellular microelec-
trodes that can measure or stimulate neuronal activity in live cells, tissue slices,
animals, or people. Implantable microelectrode arrays are placed in vivo; non-
implantable microelectrode arrays are used invitro.
Microelectrode arrays have been used to measure activity in cell cultures, brain
slices, and intact animal retinas. Recent adaptations in electrodes have facilitated
invivo recordings from rodent cortical and subcortical regions.
Microelectrode arrays have been implanted in humans for motor and sensory
neuroprostheses with promising results (see the next section). Future develop-
ments are toward bigger, faster, more powerful, and less energy-consumptive
computing chips. These may permit the development of even more complex and
competent prosthetic devices.
Brains Interfaced with Computers
The goal of neuroprosthetics is the modulation or replacement of components of
the nervous system that are disrupted in neurological injury or disorders. It
involves the use of neural interface systems (NISs). NISs are typically composed of
an implanted microelectrode array or multiple electrodes, an input or output
device, a mapping or decoding algorithm, and sensory feedback.
The most successful sensory neuroprosthesis is the cochlear implant hearing aid
(refer to Chapter14). Neural hearing loss can occur following damage to cochlear
auditory hair cells. Conductive loss and neural loss can be substantially alleviated
by cochlear implants, which are linear stimulation arrays surgically threaded into
the cochlear spiral with electrodes that directly stimulate the auditory nerves.
Here are some exciting developments:
»
Visual neuroprosthesis: A microelectrode array is implanted within the
retina. Special glasses that detect and transmit information about images are
connected to a computer that sends signals to the array to activate retinal
neurons. Higher density multiple microelectrode arrays are being developed
to provide more detailed images.
»
Motor neuroprosthesis: These strategies attempt to restore motor function
by electrical stimulation of neural components involved in the generation of
movement following injury, stroke, or neurodegeneration. Techniques include
functional electrical stimulation (FES), spinal cord stimulation (SES), and brain
computer interface (BCI). In 2018, studies combining SES with intensive
https://t.me/med1917
CHAPTER 20 Ten Technologies Revolutionizing BrainScience 379
rehabilitation enabled independent overground walking in six subjects with
spinal cord injuries.
»
BCI: BCI involves recording activity in the motor cortex and using that pattern
to control movement to bypass injury to the spinal cord. In studies with
subjects with spinal cord injuries, recorded movement control activity
patterns were delivered to the spinal cord segments to control motor output
and led to restoration of limb movements.
In a BrainGate2 clinical trial, participants with tetraplegia had microelectrode
arrays implanted in their motor cortex. Participants used an intracortical BCI
to control a computer to communicate with others via email and for web
browsing. Successful speech neuroprosthesis development is also underway.
Patients wear a high-density electrode array to capture and record neural
activity from the speech motor cortex.
»
Implantable DBS microelectrodes with closed-loop sensing systems for
longer-term use: Intracranial electrodes record brain activity in a specic
region and provide information back to a computer chip that controls the
output to stimulating electrodes. One example is the detection of an immi-
nent epileptic seizure by recording electrodes by a chip, which would then
stimulate inhibitory neurons to stop the seizure.
https://t.me/med1917
https://t.me/med1917
Соседние файлы в папке Библиотека им академика М.И. Перельмана