Theoretical Neural Model Research Articles

Alpha, delta and theta rhythms in a neural net model. Comparison with MEG data

The aim of this study is to provide information regarding the comparison of a neural model to MEG measurements. Our study population consisted of 10 epileptic patients and 10 normal subjects. The epileptic patients had high MEG amplitudes characterized with θ (4–7Hz) or δ (2–3Hz) rhythms and absence of α-rhythm (8–13Hz). The statistical analysis of such activities corresponded to Poisson distribution. Conversely, the MEG from normal subjects had low amplitudes, higher frequencies and presence of α-rhythm (8–13Hz). Such activities were not synchronized and their distributions were Gauss. These findings were in agreement with our theoretical neural model. The comparison of the neural network with MEG data provides information about the status of brain function in epileptic and normal states.

The process of learning in neural net models with Poisson and Gauss connectivities

In this study we examined the dynamic behavior of isolated and non-isolated neural networks with chemical markers that follow a Poisson or Gauss distribution of connectivity. The Poisson distribution shows higher activity in comparison to the Gauss distribution although the latter has more connections that obliterated due to randomness. We examined 57 hematoxylin and eosin stained sections from an equal number of autopsy specimens with a diagnosis of "cerebral matter within normal limits". Neural counting was carried out in 5 continuous optic fields, with the use of a simple optical microscope connected to a computer (software programmer Nikon Act-1 vers-2). The number of neurons that corresponded to a surface was equal to 0.15 mm(2). There was a gradual reduction in the number of neurons as age increased. A mean value of 45.8 neurons /0.15 mm(2) was observed within the age range 21-25, 33 neurons /0.15 mm(2) within the age range 41-45, 19.3 neurons /0.15 mm(2) within the age range 56-60 years. After the age of 60 it was observed that the number of neurons per unit area stopped decreasing. A correlation was observed between these experimental findings and the theoretical neural model developed by professor Anninos and his colleagues. Equivalence between the mean numbers of neurons of the above mentioned age groups and the highest possible number of synaptic connections per neuron (highest number of synaptic connections corresponded to the age group 21-25) was created. We then used both inhibitory and excitatory post-synaptic potentials and applied these values to the Poisson and Gauss distributions, whereas the neuron threshold was varied between 3 and 5. According to the obtained phase diagrams, the hysteresis loops decrease as age increases. These findings were significant as the hysteresis loops can be regarded as the basis for short-term memory.

Hypothalamic Neural Circuits Regulating Maternal Responsiveness Toward Infants

A theoretical neural model is developed, along with supportive evidence, to explain how the medial preoptic area (MPOA) of the hypothalamus can regulate maternal responsiveness toward infant-related stimuli. It is proposed that efferents from a hormone-primed MPOA (a) depress a central aversion system (composed of neural circuits between the amygdala, medial hypothalamus, and midbrain) so that novel infant stimuli do not activate defensive or avoidance behavior and (b) excite the mesolimbic dopamine system so that active, voluntary maternal responses are promoted. The effects of oxytocin and maternal experience are included in the model, and the specificity of MPOA effects are discussed. The model may be relevant to the mechanisms through which other hypothalamic nuclei regulate other basic motivational states. In addition, aspects of the model may define a core neural circuitry for maternal behavior in mammals.

Objective investigation of visual function using a nondestructive zoom-FFT technique for evoked potential analysis.

We describe an ultra-high resolution technique for recording evoked potentials (EPs) that are thousands of times smaller than the total EEG power. We report that two superimposed visual stimulus patterns, one modulated at F1 Hz and the other at F2 Hz, can generate 20 or more EP frequency components, each of which is contained within a bandwidth of no more than 0.004 Hz. We have developed a theoretical method for calculating the amplitudes and phases of these various cross-modulation components for different arrangements of model neurons. The relative amplitude of the various cross-modulation components seems to be a 'signature' of the particular neural model and this offers a way of testing theoretical neural models against EP data. As an illustration we compare the nonlinear EP components evoked by dichoptic stimulation with unpatterned flickering light against several models of binocular interaction. These nonlinear binocular interaction terms may offer a means of investigating binocularity in amblyopic children or infants who have low acuity in one or both eyes.