Mapping the Brain and Its Functions Integrating Enabling Technologies into Neuroscience Research (1991) / Chapter Skim
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Overview of Neuroscience Research: A Closer Look at the Neural Hierarchy
Overview of Neuroscience Research: A Closer Look at the Neural Hierarchy
Pages 48-65
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From page 48... ...
As such, the chapter describes some of the experiments that are done at each level of a vertical hierarchy of neural functioning, from behavior to genetic mechanisms (Figure 3-1~. Researchers have developed hundreds of techniques and formulated elaborate repertoires of experimental strategies to answer fundamental questions about brain functions.
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From page 49... ...
MICROCIRCUITS ~C~ ~ ~ oo ~ ~ 0 F SYNAPSE FIGURE 3-1 The neural hierarchy.
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From page 50... ...
Finally, because operant conditioning models involve learning, behavioral experiments with rats born of alcohol-ingesting mothers or rats exposed to lead poisoning have contributed to an understanding of some of the learning deficits that result from prenatal or environmental exposure to toxic substances. Other behavioral research has involved the selective destruction or electrical stimulation of discrete brain regions and the subsequent observation of behavioral changes.
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From page 51... ...
The aim of behavioral research in animals is to discover neural processes that can be correlated with human brain functions. Yet the techniques applied to human behavior have also sought to go beyond such correlations and acquire a window into cognitive and emotional function.
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From page 52... ...
recordings, which are essentially more finely tuned EEGs, contain specific waveforms that can be mapped, albeit with limited resolution, to specific structures of the brain. ERPs have been used to diagnose brain injury locations, describe abnormalities in schizophrenic patients, and trace the pathways underlying certain types of information processing.
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From page 53... ...
The systems of the brain are connected by elaborate pathways and serve many functions Although behavioral research has associated many functions with specific parts of the brain, resolution of precisely how neural computation occurs depends on knowledge of how various brain regions are connected to each other and how activity in one region affects other regions. This level of the hierarchy is concerned with organized groups of neurons "areas" of the cerebral cortex and "nuclei" of subcortical regions.
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From page 54... ...
It is common for particular neurotransmitter substances to predominate in specific brain nuclei, and thus knowledge about the actions of these neurotransmitter substances must be added to knowledge of the known anatomical connections of a particular brain region. The functional importance of the interaction of anatomical and chemical systems is particularly well illustrated in a region of the brain known as the substantia nigra.
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From page 55... ...
Throughout the past 10 years, detailed maps of the locations of scores of neurotransmitters and neuromodulators have been generated. Furthermore, techniques have been developed that combine tract tracing methods with immunocytochemistry and thus reveal simultaneously the connections and neurochemistry of discrete brain regions.
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From page 56... ...
As researchers develop new methods to encourage injured axons to regrow, such scars could present a serious barrier. The blood-brain barrier is a physical barrier between the blood and brain tissue, formed by special junctions between the cells lining the cerebral blood vessels.
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From page 57... ...
Another recently developed technique, in situ hybridization, employs specially synthesized pieces of nucleic acids that have a sequence complementary to the RNA that codes for specific proteins within neurons. These complementary pieces, which can be tagged with radioactive labels, bind to the RNA of interest; exposing brain tissue to these probes, the presence and quantity of RNA coding for specific proteins can be visualized and measured (Plate 3-4~.
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From page 58... ...
The physiology of synaptic transmission has been investigated using a variety of electrophysiological techniques in a wide range of animal species. These experiments, combined with chemical analysis, provide a rich picture of the many events that occur in the synaptic endings and in the postsynaptic neurons: ionic changes, the release of precise amounts of neurotransmitters, and actions, in the synaptic cleft, of enzymes that sometimes degrade neurotransmitters and thus end their effects.
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From page 59... ...
The synapse then "loses its strength," so that presynaptic action potentials result in decreased release of neurotransmitter. A reverse mechanism, called sensitization, helps strengthen particular inputs.
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From page 60... ...
The regulation of Sated channels gives rise to action potentials and involves many different types of biochemical reactions that have implications for all kinds of excitable membranes in the body, including skeletal and cardiac muscle cells, egg cells of the ovary, and certain immune system cells. The first step in synaptic transmission is the binding of a neurotransmitter to a receptor—similar to a key in a lock.
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From page 61... ...
FIGURE 3-3 The synthesis of cyclic adenosine monophosphate (cAMP) that results when transmitter (T)
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From page 62... ...
It is important to note that the chemical reaction cascades involving the three second messengers described here often intersect at key molecular points, allowing the different messenger systems to interact with each other. Second messenger systems are a good example of the concept that the effects of synaptic transmission are not limited to the regulation of ion channels and the resulting excitation or inhibition of action potentials.
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From page 63... ...
, which have now been sequenced, leading to a greater understanding of the structures of the genes themselves. Changes in gene expression, measured by assay of the mRNAs for each subunit, have shown that, in the developing junction between nerve and muscle, release of specific peptides from the growing axons causes activation of the acetylcholine receptor genes and stimulation of receptor synthesis.
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From page 64... ...
Although Isaac Newton discovered the color spectrum some 300 years ago, it was not until the late eighteenth century that scientists began to understand the basis of color vision: light-absorbing proteins called pigments that have overlapping but distinct sensitivities to particular wavelengths of the visible spectrum. There are three classes of cone cells: those containing red pigment, those containing green pigment, and those containing blue.
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From page 65... ...
genes for Duchenne's muscular dystrophy and neurofibromatosis have also been identified. In the case of muscular dystrophy, identification of the defective gene led to isolation of the protein dystrophin, for which the gene codes.
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