Rodney M. J. Cotterill

Cooperation of the basal ganglia, cerebellum, sensory cerebrum and hippocampus: possible implications for cognition, consciousness, intelligence and creativity

It is suggested that the anatomical structures which mediate consciousness evolved as decisive embellishments to a (non-conscious) design strategy present even in the simplest unicellular organisms. Consciousness is thus not the pinnacle of a hierarchy whose base is the primitive reflex, because reflexes require a nervous system, which the single-celled creature does not possess. By postulating that consciousness is intimately connected to self-paced probing of the environment, also prominent in prokaryotic behavior, one can make mammalian neuroanatomy amenable to dramatically straightforward rationalization. Muscular contraction is the nervous systems only externally directed product, and the signaling routes which pass through the various brain components must ultimately converge on the motor areas. The function of several components is still debatable, so it might seem premature to analyze the global operation of the circuit these routes constitute. But such analysis produces a remarkably simple picture, and it sheds new light on the roles of the individual components. The underlying principle is conditionally permitted movement, some components being able to veto muscular contraction by denying the motor areas sufficient activation. This is true of the basal ganglia (BG) and the cerebellum (Cb), which act in tandem with the sensory cerebrum, and which can prevent the latters signals to the motor areas from exceeding the threshold for overt movement. It is also true of the anterior cingulate, which appears to play a major role in directing attention. In mammals, the result can be mere thought, provided that a second lower threshold is exceeded. The veto functions of the BG and the Cb stem from inhibition, but the countermanding disinhibition develops at markedly different rates in those two key components. It develops rapidly in the BG, control being exercised by the amygdala, which itself is governed by various other brain regions. It develops over time in the Cb, thereby permitting previously executed movements that have proved advantageous. If cognition is linked to overt or covert movement, intelligence becomes the ability to consolidate individual motor elements into more complex patterns, and creativity is the outcome of a race-to-threshold process which centers on the motor areas. Amongst the ramifications of these ideas are aspects of cortical oscillations, phantom limb sensations, amyotrophic lateral sclerosis (ALS) the difficulty of self-tickling and mirror neurons.

Protein secondary structure and homology by neural networks The α-helices in rhodopsin

Neural networks provide a basis for semiempirical studies of pattern matching between the primary and secondary structures of proteins. Networks of the perceptron class have been trained to classify the amino‐acid residues into two categories for each of three types of secondary feature: α‐helix or not, β‐sheet or not, and random coil or not. The explicit prediction for the helices in rhodopsin is compared with both electron microscopy results and those of the Chou‐Fasman method. A new measure of homology between proteins is provided by the network approach, which thereby leads to quantification of the differences between the primary structures of proteins.

Thermodynamics of small clusters of atoms: A molecular dynamics simulation

The thermodynamic properties of clusters containing 55, 135, and 429 atoms have been calculated using the molecular dynamics method. Structural and vibrational properties of the clusters were examined at different temperatures in both the solid and the liquid phase. The nature of the melting transition was investigated, and a number of properties, such as melting temperature, latent heat of melting, and premelting phenomena, were found to vary with cluster size. These properties were also found to depend on the structure of the solid phase. In this phase the configuration of lowest free energy was found to be icosahedral in the 55‐atom system and face centered cubic for the two larger systems.

A novel approach to prediction of the 3-dimensional structures of protein backbones by neural networks

Three‐dimensional structures of protein backbones have been predicted using neural networks. A feed forward neural network was trained on a class of functionally, but not structurally, homologous proteins, using backpropagation learning. The network generated tertiary structure information in the form of binary distance constraints for the Cα atoms in the protein backbone. The binary distance between two Cα atoms was 0 if the distance between them was less than a certain threshold distance, and 1 otherwise. The distance constraints predicted by the trained neural network were utilized to generate a folded conformation of the protein backbone, using a steepest descent minimization approach.

Mutation screening and association analysis of six candidate genes for autism on chromosome 7q.

Genetic studies have provided evidence for an autism susceptibility locus (AUTS1) on chromosome 7q. Screening for mutations in six genes mapping to 7q, CUTL1, SRPK2, SYPL, LAMB1, NRCAM and PTPRZ1 in 48 unrelated individuals with autism led to the identification of several new coding variants in the genes CUTL1, LAMB1 and PTPRZ1. Analysis of genetic variants provided evidence for association with autism for one of the new missense changes identified in LAMB1; this effect was stronger in a subgroup of affected male sibling pair families, implying a possible specific sex-related effect for this variant. Association was also detected for several polymorphisms in the promoter and untranslated region of NRCAM, suggesting that alterations in expression of this gene may be linked to autism susceptibility.

Mammalian and avian neuroanatomy and the question of consciousness in birds.

Some birds display behavior reminiscent of the sophisticated cognition and higher levels of consciousness usually associated with mammals, including the ability to fashion tools and to learn vocal sequences. It is thus important to ask what neuroanatomical attributes these taxonomic classes have in common and whether there are nevertheless significant differences. While the underlying brain structures of birds and mammals are remarkably similar in many respects, including high brain-body ratios and many aspects of brain circuitry, the architectural arrangements of neurons, particularly in the pallium, show marked dissimilarity. The neural substrate for complex cognitive functions that are associated with higher-level consciousness in mammals and birds alike may thus be based on patterns of circuitry rather than on local architectural constraints. In contrast, the corresponding circuits in reptiles are substantially less elaborated, with some components actually lacking, and in amphibian brains, the major thalamopallial circuits involving sensory relay nuclei are conspicuously absent. On the basis of these criteria, the potential for higher-level consciousness in these taxa appears to be lower than in birds and mammals.

On the existence of pre-melting and after-melting effects A neutron scattering investigation

Abstract In order to investigate the melting transition, neutron scattering measurements have been made on aluminium and lead very near their melting temperatures. Phonon, Bragg peak, and liquid structure factor measurements are presented. The results reveal no signs of lattice instability in connection with melting, and this is discussed in the light of previous reports of premonitory effects near the melting temperature. The influence of a free surface is considered, and a new theory of surface melting is presented.

A positron annihilation study of the annealing of, and void formation in, neutron-irradiated molybdenum

Abstract Positron annihilation has been used in a study of the annealing of molybdenum irradiated at 60°C to the low dose of 1·5 × 1018 fast neutrons cm−2. On the basis of changes observed in positron lifetimes and intensities, it was possible to identify the defect mechanisms responsible for the various annealing stages. In particular it was possible to follow the growth of vacancy clusters with increasing temperature, and to establish the formation of voids above 580°C.

Molecular dynamics studies of melting: III. Spontaneous dislocation generation and the dynamics of melting

Abstract The dislocation theory of melting has been further investigated by means of dynamical computer experiments. An f.c.c. Lennard-Jones solid was taken through the melting transition, and it was found that the process is initiated by thermal generation of tiny dislocation loops of the Shockley type. The dislocation density was found to increase steadily during the transition, producing ultimately a system consisting of dislocation cores preferentially arranged as dipole loops, and predominantly in the screw orientation. A simple geometrical interpretation of Lindemanns rule emerges from the model.

Melting-point depression in very thin Lennard-Jones crystals

Abstract An f.c.c. model crystal consisting of six pseudo-infinite close-packed layers is found to melt at a temperature that is approximately 4% lower than the melting point for a crystal without surfaces. Melting starts at the free surfaces and involves the spontaneous generation of Shockley partial dislocations.