Arnold Trehub

Neuronal models for cognitive processes: networks for learning, perception and imagination.

Model neuronal mechanisms are described in detail and organized into a functional system which can perform a wide variety of high level visualcognitive tasks. A conservative estimate of the number of nerve cells required to realize the complete system in the human brain indicates that it can be accommodated within the visual areas of a single cortical hemisphere leaving a “surplus” capacity of ∼ 6·62 x 108 visual neurons in the occupied hemisphere.

Neuronal model for stereoscopic vision.

Abstract A neuronal model for stereopsis is described and simulated. Without the assumption of specific feature detectors, objects are unambiguously located in three-dimensional visual space. Random-dot stereograms are correctly resolved in depth with stimulus details conserved within planar contours.

The Brain as a Parallel Coherent Detector

Knowledge of the bioelectric signal-to-noise ratios in rat brain makes it possible to demonstrate for the first time that the brain functions as a coherent signal detector, an important class of detectors that are explicitly formulated within the statistical theory of communication. Within an afferent neuronal channel of a single modality, the brain functions as a parallel signal processor.

Adaptive pattern processing in the visual system

Proposed is a neuronal network capable of learning pattern discrimination. Basic characteristics of the component neurons largely reflect well-established physiological principles and their individual plastic properties are consistent with recent findings concerning visual experience and synaptic changes detected by electron-microscopy. Pattern discrimination within the network is robust under rather severe input-pattern degradation.

Signal characteristics of visual cortex and lateral geniculate during contralateral and ipsilateral photic stimulation

Abstract 1.1. Frequency-specific outputs from the visual cortex and lateral geniculate of unanesthetized rats were recorded and measured by means of matched narrow bandpass filters under conditions of no stimulation and bandpass-tuned flicker stimulation at the contralateral and ipsilateral eye. 2.2. In the visual cortex, output was significantly higher under stimulation than during the resting condition, and output under contralateral stimulation was significantly higher than under ipsilateral stimulation. 3.3. Signal-to-noise levels in the visual cortex were computed for both contralateral and ipsilateral stimulation. It was found that a S/N advantage of 4.38:1 favored contralateral stimulation over ipsilateral stimulation, whereas contralateral stimulation was approximately 13 times as effective as ipsilateralv with respect to the signal-to-noise power ratio. 4.4. Stimulation resulted in a significant increase in the duration of modulation periods at the visual cortex. The observed shift in modulation periods from rest to stimulation was significantly greater for contralateral stimulation compared to ipsilateral stimulation. 5.5. In the lateral geniculate, output was significantly higher under stimulation than during the resting condition, and as with the visual cortex, output under contralateral stimulation was significantly higher than under ipsilateral stimulation. 6.6. Signal-to-noise levels in the lateral geniculate showed as S/N advantage of 4.15:1 for contralateral over ipsilateral stimulation, whereas contralateral stimulation was approximately 10 times as effective as ipsilateral with respect to the signal-to-noise power ratio. 7.7. At the lateral genicualte, contralateral stimulation resulted in a significant increase in modulation period, whereas ipsilateral stimulation yielded practically no increase. 8.8. As the photo-evoked signal passed from lateral geniculate to visual cortex, S/N improved by a factor of approximately four, and the signal-to-noise power ratio by a factor of approximately ten. 9.9. The endogenous modulation period was significantly longer in the visual cortex than in the lateral geniculate. This was true under either contralateral or ipsilateral stimulation. 10.10. The known ratio of decussating optic nerve fibers in the rat was quantitatively reflected in corresponding relative signal-to-noise power ratios for contralateral and ipsilateral stimulation. This was true at both the occipital cortex and the lateral geniculate. 11.11. Modulation-period distributions in the visual cortex and lateral geniculate corresponded very well with theoretically predicted distributions derived from a proposed mathematical model.

Detection efficiency and evoked brain activity: day-to-day and moment-to-moment fluctuations

Abstract 1. 1. The relationship between fluctuations in photically evoked bioelectric brain activity and visual detection efficiency was investigated on a moment-to-moment and day-to-day basis by filtering scalp-recorded evoked brain output at the frequency of photic stimulation. 2. 2. Long term (day-to-day) changes in detection efficiency were very closely and positively correlated with long-term changes in amplitude of evoked brain output. 3. 3. Moment-to-moment fluctuations in detection efficiency were not correlated with moment-to-moment fluctuations in amplitude of evoked brain output. 4. 4. It is suggested that the scalp-recorded evoked response of the brain reflects changes in general arousal but does not reveal fluctuations in attention per se.

Associative sequential recall in a synaptic matrix

Abstract An adaptive neuronal network (synaptic matrix) was simulated. After learning a number of randomly generated scenes, the network was tested for associative sequential recall in a stimulus-bound mode and in an image-bound mode. It is demonstrated that neuronal mechanisms of this kind can exhibit orderliness or looseness of associative response suggestive of human recall behavior.

First-occupancy model for signal transfer in the brain

Abstract In rats and rabbits, optic nerve fibers are asymmetrically decussated. Evoked bioelectric signal/noise power ratio as a function of decussation ratio afferent to the lateral geniculate and thence to visual cortex conforms approximately to what one would expect if the visual system functioned as a parallel coherent detector. Brain mechanisms which can quantitatively account for these findings have not been previously proposed. A theoretical model is proposed to explain observed bioelectric input-output relationships in asymmetrically decussated visual systems and to suggest a general mechanism for signal transfer in the mammalian brain. The model is stochastic and is based upon earlier work concerning coherent neuronal activity. A specific quantitative implication of the model is that, on the average, three ganglion cells in the retina will drive each principal cell in the lateral geniculate. This prediction of the model is verified by recent experimental findings.