Humans brain

Since the early 20th century, chemists have represented molecular information by molecular models. The human brain comprehends these representations of graphical models with 3D relationships more effectively than numerical data of distances and angles in tabular form. Thus, visualization makes complex information accessible to human understanding easily and directly through the use of images. 

Just like humans, ANNs learn from examples. The examples are delivered as input data. The learning process of an ANN is called training. In the human brain, the synaptic connections, and thus the connections between the neurons. 

Concomitantly with the increase in hardware capabilities, better software techniques will have to be developed. It will pay us to continue to learn how nature tackles problems. Artificial neural networks are a far cry away from the capabilities of the human brain. There is a lot of room left from the information processing of the human brain in order to develop more powerful artificial neural networks. Nature has developed over millions of years efficient optimization methods for adapting to changes in the environment. The development of evolutionary and genetic algorithms will continue. 

The human brain is comprised of many millions of interconnected units, known individually as biological neurons. Each neuron consists of a cell to which is attached several dendrites (inputs) and a single axon (output). The axon connects to many other neurons via connection points called synapses. A synapse produces a chemical reaction in response to an input. The biological neuron fires if the sum of the synaptic reactions is sufficiently large. The brain is a complex network of sensory and motor neurons that provide a human being with the capacity to remember, think, learn and reason. 

It is tempting to view ANNS as simplified versions of biological nervous systems. Yet even the most complex neurocomputers, with several million neurons, are unable to mimic the behavior of a fly, which has approximately one million nerve cells. This is because the nerve system of the fly has far more interconnections than are possible with current-day neurocomputers, and their neurons are highly specialized to perform necessary tasks. The human brain, with about 10 billion nerve cells, is still several orders of magnitude more complex. 

Perhaps the quintessential example of a complex system is the human brain, which, consisting of something on the order of 10 neurons with lO -lO coniiec-... 

The human brain is a neural net consisting of about ten billion interconnected neurons. Figure 10.1-a shows a schematic representation of a single neuron. At the ri.sk of grossly oversimplifying the brain s enormously complex physiology, we will only focus on a relatively few functional parts of a single neuron. 

Consider the basic probkun of how information is distributed throughout a system, and the manner in which it is retrieved. We. know that in a conventional computer, for example, information is stored in random-access memory (RAM). This means that the memory address of where the information actually exists and the information itself are uncorrelated. In order to retrieve the information, one must know its address exactly, as even the slightest error renders that information effectively unretrievable. In particular, it is in general impossible to retrieve RAM data if armed only with a partial knowledge of its address. In contrast, associative memories (sometimes also called content-addressable memories), much like the form of memory believed to be used by human brains, are such that they can be completely retrieved even when searched for with partial information,... 

Human brain natriuretic peptide (BNP) is a small peptide of 32 amino acids used in the treatment of congestive heat failure. How many nitrogen bases are present in the DNA that codes for BNP ... 

Hi-receptors in the adrenal medulla stimulates the release of the two catecholamines noradrenaline and adrenaline as well as enkephalins. In the heart, histamine produces negative inotropic effects via Hr receptor stimulation, but these are normally masked by the positive effects of H2-receptor stimulation on heart rate and force of contraction. Histamine Hi-receptors are widely distributed in human brain and highest densities are found in neocortex, hippocampus, nucleus accumbens, thalamus and posterior hypothalamus where they predominantly excite neuronal activity. Histamine Hrreceptor stimulation can also activate peripheral sensory nerve endings leading to itching and a surrounding vasodilatation ( flare ) due to an axonal reflex and the consequent release of peptide neurotransmitters from collateral nerve endings. 

As early as 1961, the first generation of MAO inhibitors (iproniazid, isocarboxazide) were employed for the treatment of Parkinson s disease (PD). However, because of the severe side effects, such as cheese reaction, they were abandoned. The realization that the basal ganglia (extrapyramidal region) of human brain contained mostly MAO-B, which metabolized... 

Neuronal NO synthase (nNOS) is constitutively expressed in neurons of the brain. Its activity is regulated by Ca2+ and calmodulin. Half-saturating L-arginine concentrations are around 2 pM. cDNAs encoding nNOS have been cloned from rat and human brain. The open reading frame of human nNOS consists of 4299 bp, corresponding to 1433 aa. This predicts a protein of 160 kDa, which is in accordance with the molecular mass of the purified protein. 

FIGURE 2 An MRI image of a human brain. The patient must lie within the strong magnetic field. The detectors can be rotated around the patient s head, thereby allowing many different views to be recorded. 

Freedman, M.S., Ruijs, T.C., Selin, L.K., Antel, J.P. (1991). Peripheral blood gamma delta T cells lyse fresh human brain derived oligodendrocytes. Ann. Neurol. 30, 794-800. 

Ball JC, Lange WR, Myers CP, et al Reducing the risk of AIDS through methadone maintenance treatment. J Health Soc Behav 29 214—226, 1988b Bare LA, Mansson E, Yang D Expression of two variants of the human mu opioid receptor mRNA in SK-N-SH cells and human brain. FEES Lett 354 213—216, 1994 Barr HL, Cohen A Abusers of alcohol and narcotics who are they Int J Addict 22 52 5— 541, 1987... 

Paris D, Ait-Ghezala G, Mathura VS, Patel N, Quadros A, Laporte V, et al. Anti-angiogenic activity of the mntant Dntch A(beta) peptide on human brain microvascular endothelial cells. Brain Res Mol Brain Res 2005 136 212-30. 

T. Greitz. D. H. Ingvar. and L. Widen (Eds.), The Metabolism of the Human Brain Studied with Positron Emission Tomography, Raven Press, New York, 1985. 

Homocarnosine (Figure 31-2), present in human brain at higher levels than carnosine, is synthesized in brain tissue by carnosine synthetase. Serum carnosinase does not hydrolyze homocarnosine. Homocarnosinosis, a rare genetic disorder, is associated with progressive spastic paraplegia and mental retardation. 

Liver, the major site of purine nucleotide biosynthesis, provides purines and purine nucleosides for salvage and utilization by tissues incapable of their biosynthesis. For example, human brain has a low level of PRPP amidotransferase (reaction 2, Figure 34-2) and hence depends in part on exogenous purines. Erythrocytes and polymorphonuclear leukocytes cannot synthesize 5-phosphoribosylamine (strucmre III, Figure 34-2)... 

Walsh, V. 2000 Reverse engineering the human brain. Phil. Trans. R. Soc. Lond. A 358, 497-511... 

---