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H Stowell

Publications and source records attributed to H Stowell.

At least 19 recordsLinked to original sources
PubMed1990

Constraint and pathology in spontaneously activated systems.

Neural network modeling is approaching a strange attractor. Mathematical demonstrations of the theoretical behavior of non-Lipschitzian dynamical systems claim to show how such self-developing computational networks may be fully deterministic as to their microstructure yet without any prescription of their final state in advance. Justification for these simulations stems from applications which demand more biological realism in the design of neurobiotics. Realization of such modeling in actual hardware does not exist. While the best of these models are surely heuristic for neuroscientists who want to know how brains work, their attempted realization in control systems for planetary high technology seems confounded by several intractable problems, which, a few years ago, would have interested only neurophilosophers in retirement.

Artificial Intelligence↗
PubMed1990

Time and tiles on the brain.

Both the quasicrystalline appearance of mammalian cerebral cortex and the quasiperiodicity of mammalian cerebral compound field potentials (EEG/ERBP) have long been noted. A recent experiment claims to show the eigenvalue spectrum of a quasiperiodic tiling of coupled oscillators in the plane; and this spectrum of resonant frequencies has some analogies with that of mammalian EEG/ERBP. Concurrently, Connectionist literature now admits the significance of internally generated network rhythmicity in Non-Lipschitzian neurodynamics. It may be time to test the hypotheses of: (a) quasi-crystalline icosahedral symmetry of neocortical architectonics and (b) some fractal characteristics of EEG/ERBP under behavioral conditions.

Animals↗
PubMed1990

Cerebral rhythms and temporal coherence.

Some studies of scalp-conducted human EEG show a positive correlation between the temporal coherence of prestimulus activity in the theta, alpha, and beta passbands, on the one hand, and both target probability and subjective self-report about good performance, on the other. There remains an important ambiguity in these data: Are these changes in temporal coherence merely a reflection of changes in subjective relaxation, or do they index the timing of neural network convergences to terminal attractors? Other studies of human EEG during temporal conditioning paradigms suggest that the second alternative can be rigorously tested.

Brain↗
PubMed1990

Temporal coherence of superimposed EEG waves: a problem in nonlinearity.

Traditional "stimulus-time-locked signal averaging" of human EEG, as usually practiced in both clinical and basic contexts, assumes the superposition principle of algebraic summation for a linear time series. But there are now experimental data on nonlinear coupling of neural populations in the brains of two species, and reasons for regarding human EEG as a nonlinear, chaotic time series, reflecting a global mixture of subharmonics and harmonics of continually varying "fundamental" frequencies within the commonly observed power spectrum of a subject attending to sensory input (about 3-35 Hz). So we must ask ourselves if the established conventions for averaging and temporal comparison of both scalp-conducted voltages and related magnetic fluxes from human heads are appropriate for the suspected nonlinear coupling of neural oscillators.

Electroencephalography↗
PubMed1989

Connectionism and an inescapable defect.

Linear connectionist models of neurocomputing show how input patterns may be recognized, stored, compared, and recalled for output in serial-parallel, quasi-Hebbian networks. This aids the design of hardware and software for better robotics, while offering useful insights to neuroscientists studying sensorimotor systems, but connectivity via quasi-Hebbian nodes and back-propagation layers alone cannot show us how vertebrate cerebellum, allocortex, and neocortex work.

Animals↗
PubMed1987

How to use EEG/ERBP phenomena.

Hitherto the study of cerebral slow waves has been mainly empirical phenomenology, in spite of 50 years of effort to discover their origins and possible functions. Since 1970 the increasing use of both analog and digital filters, combined with more sensitive averaging techniques, has led to better understanding of some possible functional significance for the electroencephalogram (EEG) and the endogenous slow waves of event-related brain potentials (ERBP). The developing concepts and mathematics of non-linear dynamicsand coupled oscillators, when considered in the light of cerebral circuit geometry and topology, of local neuronal circuitry, and of both observed and experienced biological behavior, now offer hope for future, more complete, understanding of the development of 'conscious and goal-directed' activity from robotic and reflexive stimulus-response paradigms. Immediate practical results of a biophysical approach to brain waves should be: Models of vertebrate brains as distributed systems of non-linearly coupled oscillators; and revision of traditional methodologies for recording and interpreting EEG/ERBP data.

Afferent Pathways↗
PubMed1987

Computation, rhythm, and cerebral slow waves.

The trajectories of data and modelling from formerly divergent research efforts now seem to be converging to an unexpected region of the phase space of neuroscience. Computational network theory and simulation assume that temporal rhythm may be a significant parameter for the successful organization of nonlinear analog computation effected by hierarchical sets of biological neurons and of nonbiological circuitry alike. For neurobiology, the apparently chaotic rhythms of cerebral compound field potentials--the electroencephalogram (EEG) and slow waves of event related brain potentials (ERBP)--have long been a phenomenological embarrassment, of only marginal clinical utility. But recent data from molecular biophysics, nonlinear dynamics, artificial intelligence, and scalp-conducted human electrocorticography suggest a possible functional role in the serial gating of neural network computations for the familiar theta-alpha-beta rhythms of the EEG clinic.

Auditory Perception↗
PubMed1987

Are cerebral slow waves necessary?

A neurosurgical study of the human somatosensory evoked potential suggested, over 13 years ago, that the early fast waveform recorded by averaging on SI cortex in response to electrical stimulation of the skin is insufficient for a conscious report of tactile sensation. The same study also implied that the succeeding slower waveform, showing consistent averaged timing between 50 and 100 ms after onset of the transient stimulus, was necessary (though perhaps insufficient) for a report of sensation. Since these data seem not to have been denied or confirmed, it may be useful to report hitherto unpublished data on scalp-conducted somatosensory evoked potentials which tend to confirm the direct cortical results, insofar as conventional coherent averages can make any valid contribution to the problem of the sequence of electrophysiological events in laminar cortex when afferent information arrives from the periphery.

Evoked Potentials, Somatosensory↗
PubMed1987

Denying behavior: throwing experience out.

A recent paper (Skarda, 1986) from a distinguished laboratory of experimental neurophysiology denies the classical concept of neural representation. According to this essay, which is itself a critique of a basic neuroscientific assumption as implied in a new book about the mind-brain problem, it is wrong to suppose that patterns of neural activity represent anything. Representations should be replaced by "self-organizing neural processes that achieve a certain end-state of interaction between the organism and its environment in a flexible and adaptive manner." Although this alternative wording is neither surprising nor radical, and would prove acceptable to most biologists as an adequate description of one important aspect of organized cellular activity, its author's dogmatic denial of "representation" as a metaphor for other important aspects of living behavior seems both surprising and unnecessary.

Behavior↗
PubMed1987

Cerebral slow waves and time parsing.

Cerebral compound field potentials, observed as either the electroencephalogram (EEG) or stimulus-synchronized event related brain potentials (ERBP), have received thirty years of experimental study as possible indicators of general brain state or of sensorimotor information processing respectively. They have received relatively little attention in the context of subjective awareness of a undirectional dimension of time, and then mainly in relation to nonhuman sensorimotor rhythms and hippocampal theta waves. This report is a pilot study of human EEG and ERBP during subjective familiarization with simple motor-sensory temporal patterns, using both small-averaged and unaveraged time series of the traditional theta-alpha-beta band and computer-unaided, human recognition of temporal patterns in the cerebral slow waves. The data support experimental use of more sophisticated methods to analyze possible time-parsing functions of primate extracellular field oscillations.

Adult↗
PubMed1985

IQ revisited in the time domain: a critique or irresponsible brainwaves.

In 1969 two authors proposed that human visual evoked potentials could be predictors of psychometrically scored "intelligence." This interpretation of their data was subsequently invalidated. In 1982 two other authors made a similar claim for auditory evoked potentials; their published methodology and general theoretical background in sensory neurophysiology suggest even less likelihood of predictive validation.

Brain↗
PubMed1985

Human evoked potentials and C-fiber pain.

An evoked potential report by four authors has revived the question of the somatosensory specificity of the vertex potential of somatosensory evoked potentials, when these are derived by scalp conductance in response to subjectively painful skin stimulation. By a peripheral nerve-block maneuver combined with subjective sensoriperceptual reports, the authors show a late, slow positive wave in the somatosensory evoked potential whose appearance and disappearance are claimed to reflect the brain's response to a uniquely C-fiber input and to a combination of A delta and C-fiber input respectively. But their idiosyncratic interpretation of their data has merely revived an unresolved question: How much, if anything, of these familiar "ultralate," slow positivities can be ascribed to any form of neural encoding of nociception, as distinct from a nonspecific brain response to a behaviorally important stimulus?

Animals↗