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Nervous System

Connectome Phrenological Map Connectome (ome = whole) means the entire neuronal connections in the brain, human and otherwise. It is suggested that such wiring diagram of the brain would reveal the mind - the sums of the senses, actions, thoughts, and memories. The idea is the extension of earlier effort by checking on the brain anatomy (Figure 01) and connecting them to various functions. The phrenological map (Figure 02) appeared in the 1800's represents one of such attempts. The image on the right in Figure 01 shows the major anatomical connections using MRI in 2008. The middle diagram is a computer model of the human connectome generated by network science tools.

Figure 01 Connectome
[view large image]

Figure 02 Phrenological Map [view large image]

Connectome of C. elegans So far up till 2014, only one connectome has been completely constructed from the 1 mm long C. elegans roundworm, which possesses only 302 neurons. Very thin slices of about 50 nm thick (about 20 thousand pieces) were scanned by electron microscope, and it took 12 years to identify the neurons by lining them up one slice after the other. Based on such experience, it will take about one million person-year to re-construct just 1 mm3 of the cortex. Anyway, Figure 06 illustrates just a small part of the neural circuit in the worm, which regulates oxygen homeostasis by mounting sophisticated behavioural responses to ambient O2, avoiding both too high (atmospheric) and too low (hypoxic) levels (see explanation in the diagram).

Figure 06 Connectome of C. elegans [view large image]

The Human Connectome Project (HCP) was launched in 2009. Its aim is to trace the brain's long-range communication network using two main techniques, both of which rely on magnetic resonance imaging (MRI) to obtain data from living people. The "connectome" is a web of nerve-fibre bundles that criss-cross the brain in their thousands and form the bulk of the brain's white matter. It relays singals between specialized regions devoted to functions such as sight, hearing, motion and memory, and ties them together into a system that perceives, decides and acts as a unified whole. If a standard map of the connections can be produced from the average, it can be used to shed light on what the variations
Connectome Project might mean for qualities such as intelligence or sociability, and possibly reveal what happens if the network goes awry. It is believed that brain disorders - from schizophrenia to depression to post-traumatic stress disorder - are disorders of connectivity. One of the two techniques is Diffusion-Spectrum Imaging (DSI), which traces the direction of water molecules moving in the brain (Figure 07). This method maps out the structure of the brain. Although it seems that the nerve fibers are arranged in regular 3-D grid as shown in the brain image, we still have to figure out what they are there for (just like the entangled cables in the computer room)? Thus the second method of resting-state functional MRI (re-fMRI) is required to look for activated brain regions without the participants to carry out a specific cognitive task such as in fMRI. It is assumed that the increase in blood flow is related to brain activity. In re-fMRI, there is no task, it is instead assumed that correlations

Figure 07 Connectome, Project [view large image]

among the activity levels in different areas are linked. This method looks for specific function preformed by different area of the brain (Figure 07). The two methods together would allow construction of standard connectome to identify the wiring with functions. See "Connectome" by Sebastian Seung for detail.

It is well known that every location of the cerebral cortex can be described by many structural characteristics and functions. For examples, the task-based functions and resting state are mapped by fMRI, while the cortical architecture is related to the myelin density.

Uni- to Multi- Modal Brain Maps Recently in 2016, the HCP using high-quality MRI produces a multi-modal (many kinds of measurements) map comprising the properties of architecture, function, connectivity and topography into every location of the cortex (Figure 08). The data were gathered from 210 healthy young adults, the "average" cortex is divided into 360 areas (180 for each hemisphere).

Figure 08 Uni- to Multi- Modal Brain Maps
[view large image]

Figure 09 displays a counter-clockwise rotating sequence of the left hemisphere, starting from the outside (a), to the front (b), onto the inside (e), the rear (g), and back (h). Figure 10 provides further explanation :
HCP Brain Maps, Rotating Views HCP Brain Maps, Examples
  • The images include both inflated left and right hemispheres and flattened cortical surfaces.
  • Black outlines indicate borders of the 180 areas.
  • Color codes : red (auditory), green (somato-sensory), blue (visual); each area may be colored as a mixture.
  • White means task positive, while black is task negative.
  • The insert is an illustruation of the 3D color space.

Figure 09 HCP Brain Maps, Rotating Views [view large image or a video]

Figure 10 HCP Brain Maps, Examples [view large image]

  • Areas : LIPv, MT (b, g); POS2, RSC (b, r); V1 (b); A1 (r); while 55b, PSL, SFL, 44 are language-related.

The oval shaped area in Figure 10 is the interface to the putamen and caudate nucleus, which are small parts of the subcortical structure (Figure 11). In addition, the putamen and globus pallidus form the lentiform nucleus. All these are compnents of the structures that comprises the
Subcortical Structure Basal Ganglia basal ganglia (Figure 12). The main function of these areas is to regulate movements and influence various types of learning. It is thus task positive (response to attention-demanding tasks) in nature and colored white in Figures 09 and 10.

Figure 11 Subcortical Structure [view large image]

Figure 12 Basal Ganglia [view large image]
putamen (red) + caudate nucleus

LImbic System Stria Terminalis Figure 13 illustrates the relative locations between the basal ganglia and the limbic system, which is further inside at the center of the brain. The hippocampus (relates to memory formation) and the stria terminalis (correlates with anxiety) wind their ways from the center to the temporal lobe in the cortex where they end up at the tip of the caudate nucleus. The tanglement creates a lot of confusion in the lateral view of a 2-dimensional brain map. For example, the amygdala (responsible for emotion) is supposed to be part of the fibrous stria terminalis (Figure 14) but showed up at the tail end of the caudate nucleus in the lateral views of Figures 11 and 12.

Figure 13 Limbic System

Figure 14 Stria Terminalis

See "Higher Functions" for the roles play by the frontal lobes in addition to the five senses in the rest of the cortex as determined by 20th century neuro-scientists.

Anyway, it is pointed out that the 360 areas in the HCP brain map are not the final designations, the number as well as boundary would be altered by further research works. A key innovation in the current study is an automatic algorithm that produces "biomarkers" (indicator for some kind of bio-activity) for individual to diagnose mental disease or peculiar behavior for example. The aim of this kind of research is to elucidate the neural pathways that underlie brain function and behavior.

See original article : "A Multi-modal Parcellation of Human Cerebral. ".

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