Theodore H. Bullock

Induced rhythms in the brain

to Induced Rhythms: A Widespread, Heterogeneous Class of Oscillations.- Oscillations in the Striate Cortex.- 1 Mechanisms Underlying the Generation of Neuronal Oscillations in Cat Visual Cortex.- 2 Stimulus-Specific Synchronizations in Cat Visual Cortex: Multiple Microelectrode and Correlation Studies from Several Cortical Areas.- Cortical Rhythms, Ongoing (EEG) and Induced (ERPs).- 3 The Rhythmic Slow Activity (Theta) of the Limbic Cortex: An Oscillation in Search of a Function.- 4 Is There any Message Hidden in the Human EEG?.- 5 Event-Related Synchronization and Desynchronization of Alpha and Beta Waves in a Cognitive Task.- 6 Magnetoencephalographic Evidence for Induced Rhythms.- 7 Rostrocaudal Scan in Human Brain: A Global Characteristic of the 40-Hz Response During Sensory Input.- 8 Evoked Potentials: Ensembles of Brain Induced Rhythmicities in the Alpha, Theta and Gamma Ranges.- 9 Predictions on Neocortical Dynamics Derived from Studies in Paleocortex.- 10 A Comparison of Certain Gamma Band (40-HZ) Brain Rhythms in Cat and Man.- 11 Human Visual Evoked Potentials: Induced Rhythms or Separable Components?.- Thalamic Oscillations.- 12 Network Properties of the Thalamic Clock: Role of Oscillatory Behavior in Mood Disorders.- 13 Mesopontine Cholinergic Systems Suppress Slow Rhythms and Induce Fast Oscillations in Thalamocortical Circuits.- 14 Oscillations in CNS Neurons: A Possible Role for Cortical Interneurons in the Generation of 40-Hz Oscillations.- Cellular and Subcellular Mechanisms Based on Invertebrate and Simple Systems.- 15 Modification of Oscillator Function by Electrical Coupling to Nonoscillatory Neurons.- 16 Biological Timing: Circadian Oscillations, Cell Division, and Pulsatile Secretion.- 17 Comparison of Electrical Oscillations in Neurons with Induced or Spontaneous Cellular Rhythms due to Biochemical Regulation.- 18 Signal Functions of Brain Electrical Rhythms and their Modulation by External Electromagnetic Fields.- Theories and Models.- 19 Inhibitory Interneurons can Rapidly Phase-Lock Neural Populations.- 20 The Problem of Neural Integration: Induced Rhythms and Short-Term Correlations.- 21 Flexible Linking of Visual Features by Stimulus-Related Synchronizations of Model Neurons.- 22 Synergetics of the Brain: An Outline of Some Basic Ideas.- Epilogue.- Brain Natural Frequencies are Causal Factors for Resonances and Induced Rhythms.

Pacemaker Neurons: Effects of Regularly Spaced Synaptic Input

The consequences of inhibitory or excitatory synaptic input between pacemaker neurons were predicted mathematically and through digital-computer simulations, and the predicted behavior was found to occur in abdominal ganglia of Aplysia and in stretch receptors of Procambarus. Discharge patterns under conditions that do not involve interneuronal feedback are characteristic and self-stabilizing. Paradoxically, increased arrival rates of inhibitory input can increase firing rates, and increased excitatory input rates can decrease firing rates.

Coding properties of two classes of afferent nerve fibers: high-frequency electroreceptors in the electric fish, Eigenmannia.

THE PROPOSITION THAT neurons can encode information about the intensity of stimuli in other ways than by the familiar gradation of intervals between impulses has been put forward (5, 6, 12). Perkel and Bullock (23) catalog the known and the candidate codes by which neurons can represent information in streams of nerve impulses. For none of these, other than the familiar frequency coders, is a quantitative characterization available of the behavior of the impulse train as a function of intensity.

The Jamming Avoidance Response of High Frequency Electric Fish

Using a frequency difference (Δ F) clamp to maintain a stimulus and frustrate the normal escape from a jamming frequency, the response is found to be a characteristic function of the ΔF between stimulus and fish (Figs. 2, 3, 4, 6). It is graded on both sides of a best ΔF of about 3 Hz (= 0.3% in Sternarchus, 1.0% in Eigenmannia). There is no systematic response when F stimulus = F fish, regardless of phase.

The phylogenetic distribution of electroreception: evidence for convergent evolution of a primitive vertebrate sense modality.

Specializations for electroreception in sense organs and brain centers are found in a wide variety of fishes and amphibians, though probably in a small minority of teleost taxa. No other group of vertebrates or invertebrates is presently suspected to have adaptations for electroreception in the definition given here. The distribution among fishes is unlike any other sense modality in that it has apparently been invented, lost completely and reinvented several times independently, using distinct receptors and central nuclei in the medulla. There are so far no clearly borderline or transitional fishes, either physiologically or anatomically. We rather expect a few new electroreceptive taxa to be found. The evoked potential method and the newly validated central anatomical criteria provide two useful tools for searching. Although Myxiniformes probably lack electroreception, it is well developed in Petromyzoniformes and in all other non-teleost fishes except Holostei. Thus Elasmobranchia, Holocephala, Dipneusti, Crossopterygii, Polypteriformes and Chondrostei have the physiological and anatomical specializations in a common form consistent with a single origin in primitive vertebrates. Amphibian ancestors probably inherited the system from a stem similar to one of these and passed it on at least to the ambystomatoid and salamandroid urodeles, apparently after losing the kinocilium of the sense cell. The suggestion of electroreception in ichthyophid apodans from skin histology has not been confirmed physiologically, behaviorally or by brain anatomy. With respect to more advanced fishes the most parsimonious interpretation is that the entire system, peripheral and central was lost in ancestors of holostean and teleostean fishes and new systems reinvented in Siluriformes, in Gymnotiformes, in Xenomystinae and in Mormyriformes. These 4 taxa must represent at least two, and probably 3 or 4 independent inventions, presumably from mechanoreceptive lateral line organs and brain centers.

EEG coherence has structure in the millimeter domain: subdural and hippocampal recordings from epileptic patients

Subdural recordings from 8 patients and depth recordings from 3 patients via rows of electrodes with 5-10 mm spacing were searched for signs of significant local differentiation of coherence calculated between all possible pairs of loci. EEG samples of 2-4 min were taken during 4 states: alertness, stage 2-3 sleep, light surgical anesthesia permitting the patient to respond to questions and electrical seizures. Coherence was computed for all frequencies from 1 to 50 Hz or 0.3-100 Hz; for comparisons the mean coherence over each of 6 or 7 narrower bands between 2 and 70 Hz was used. Whereas the literature supports the view that EEG coherence is usually substantial over many centimeters, the hypothesis here tested--and found to be well above stochastic expectations--is that significant structure occurs in the millimeter domain for EEG recorded subdurally or within the brain. In both the subdural surface samples and those from temporal lobe depth electrode arrays coherence declines with distance between electrodes of the pair, on the average quite severely in millimeters. This is nearly the same for all frequency bands. For middle bands like 8-13 and 13-20 Hz, mean coherence typically declines most steeply in the first 10 mm, from values indistinguishable from 1.0 at < 0.5 mm distance to 0.5 at 5-10 mm and to 0.25 in another 10-20 mm in the subdural surface data. Temporal lobe depth estimates decline about half as fast; coherence > or = 0.5 extends for 9-20 mm and > or = 0.25 for another 20-35mm. Low frequency bands (1-5, 5-8 Hz) usually fall slightly more slowly than high frequency bands (20-35, 35-50 Hz but the difference is small and variance large. The steepness of decline with distance in humans is significantly but only slightly smaller than that we reported earlier for the rabbit and rat, averaging less than one half. Local coherence, for individual pairs of loci, shows differentiation in the millimeter range, i.e., nearest neighbor pairs may be locally well above or below average and this is sustained over minutes. Local highs and lows tend to be similar for widely different frequency bands. Coherence varies quite independently of power, although they are sometimes correlated. Regional differentiation is statistically significant in average coherence among pairs of loci on temporal vs frontal cortex or lateral frontal vs. subfrontal strips in the same patient, but such differences are usually small.(ABSTRACT TRUNCATED AT 400 WORDS)

Revisiting the Concept of Identifiable Neurons

Although eutely in nematodes was known, giant neurons in several taxa and unique motor neurons to leg muscles in decapod crustaceans, the idea that many animals have many identifiable neurons with relatively consistent dynamical properties and connections was only slowly established in the late 1960s and early 1970s. This has to be one of the important quiet revolutions in neurobiology. It stimulated a vast acquisition of specific information and led to some euphoria in the degree and pace of understanding activity of nervous systems and consequent behavior in terms of neuronal connections and properties. Some implications, problems and opportunities for new discovery are developed. The distribution of identifiable neurons among taxa and parts of the nervous system is not yet satisfactorily known. Their evolution may have been a case of several independent inventions. The degree of consistency has been quantified only in a few examples and the plasticity is little known. Identified neurons imply identifiable circuits but whether this extends to discrete systems, functionally definable, seems likely to have several answers in different animals or sites. Very limited attempts have been made to extend the concept to cases of two or ten or a hundred fully equivalent neurons, on all kinds of criteria. These attempts suggest a much smaller redundancy and vaster number of types of neurons than hitherto believed. Theory as well as empirical information has not yet interpreted the range of systems from those with small sets of relatively reliable neurons to those with large numbers of parallel, partially redundant units. The now classical notion of local circuits has to be extended to take account of and find roles for the plethora of integrative variables, of evidence for neural processing independent of spikes and classical synapses, of spatial configurations of terminal arbors and dendritic geometry, of modulators and transmitters, degrees of rhythmicity (regularity varying several orders of magnitude), and of synchrony. Adequate language and models need to go beyond ‘circuits’ in any engineering sense. Identifiable neurons can contribute to a broad spectrum of issues in neurobiology.

Lateral coherence of the electrocorticogram: a new measure of brain synchrony

As one test of the idea that compound field potentials in higher centers have a fine structure, the horizontal extent of coherence (C) was studied on the brain surface, with many closely spaced semimicroelectrodes in rabbits and rats. On the average C tends to fall with distance (D) in the 0.5-10 mm range; apart from driven rhythms, C usually falls to noise level at D greater than 10 mm. A useful measure is D (mm) where C has fallen to 0.5 (DC = 0.5); for most F bands within the range 1-50 Hz this is usually 2.5-5 mm, averaging over the neocortex in both species. Synchrony for neural tissue should mean a degree of congruence in a population (not a 2-point correlation); decline of C with D can measure synchrony by reflecting the volume at or above a specified C. Sleeping and waking mammals, an invertebrate (Aplysia), a ray, and a reptile were compared in degrees of synchrony; this cannot be judged by eye and is found sometimes hardly different between high-voltage-slow and low-voltage-fast states. Aplysia has negligible synchrony; the ray and lizard may be intermediate. C maps show patchiness superimposed on the general decline with D; no obvious pattern between parts of the cortex is consistent among individuals. Factors influencing variance, repeatability and extent of significant C are assessed. Brain size, passive spread, electrode size (at least 1-100 microns) and closeness of contact with pia mater rarely contribute materially, even within 1 mm. C commonly falls moderately with frequency (F) from a maximum between 1 and 8 Hz, usually without consistent peaks except for special cases of driving rhythms, such as theta. Intracortically the distribution of C is more local, both radially and horizontally. Although it was not possible to say when the two electrodes were in the same lamina, most laminae are highly coherent with all others. One or two sharp radial discontinuities in C are common, often but not consistently in the middle layers. C shows no simple relation to distance. In spite of the prevalent high coherence between laminae, radially, C varies widely horizontally from low to high in the 0.1-1 mm range. C is regarded as one aspect of cooperativity in a cellular dynamic system with fine structure in the fractional millimeter and second range; so far we are observing it with severely distorting smoothing procedures.

The Auditory Brain Stem Response in Five Vertebrate Classes

In representative elasmobranchs, osteichthyans, amphibians, reptiles and birds, average evoked potentials in response to acoustic clicks and tone bursts were recorded intracranially, but outside the brain, or extracranially. Controls against artifacts and tests after transections show that these potentials conform to criteria for auditory brain stem responses (ABRs). Brief waves in a 10-15 msec sequence originate successively in the eighth nerve, medulla and midbrain; there is little contribution to the latter waves from the lower levels. This response pattern appears to be consistent within each species and is similar to that extensively studied in mammals. Some of its features are remarkably alike in all the vertebrate classes tested, implying a generality in the existence of a subset of auditory neurons at several brain levels that are highly synchronous in activity, even after several synapses, and geometrically oriented to add their macroscopic, open, dipole fields. The intensity, repetition rate and the power spectrum of the click stimuli have little effect on the ABR pattern, except when the peak energy is in the low frequency range. In the range below ca. 700 Hz frequency content has a considerable effect; lower frequencies broaden certain waves. Cooling has marked and differential effects on component processes. Reversing click phase, e.g. from initial compression to initial rarefaction, can show no effect or any of several effects, depending on the species. Tone bursts evoke onset ABRs and in some cases after a transitional period a sustained frequency following response. The ABR resembles a click evoked potential even when stimulus rise time is slow. Background tones of particular frequency are most efficient in masking click evoked ABRs; white noise is less efficient. The ABR should be useful in neuroethology since it can be studied without invading the brain. It can tell that the brain is sensitive to a sound. In an immobilized animal it can be recorded in a single sweep, or it can be averaged from an awake tethered animal. It shows good sensitivity and at least some correspondence with behavioral measures of hearing.

Diverse forms of Activity in the Somata of Spontaneous and Integrating Ganglion Cells

With the introduction of the lobster cardiac ganglion into the service of physiology by Welsh and Maynard (1951) and Maynard (1953a—c, 1954, 1955), an extremely valuable preparation for the analysis of the properties and mechanisms of organized groups of neurones became available. Maynard has studied particularly the organization of the normal burst which initiates each heart beat and the consequences of stimulation of the extrinsic inhibitor nerve from the central nervous system, which he found to contain a single inhibitory axon on each side. These studies with extracellular macro-electrodes, partly confirmed by Matsui (1955), have shown: (a) that the ganglion, consisting of nine cells of complex form (Fig. 1 and Alexandrowicz, 1932), is capable of initiating at regular intervals complex bursts consisting of several to many impulses in each cell; (b) that there is a distinct pattern in the whole complex as well as in the bursts of impulses in each unit; and (c) that there is a division of labour among the ganglion cells. Certain of the cells apparently normally initiate the burst which represents one heart beat, others, although capable of spontaneous firing, apparently normally follow. These latter certainly, and possibly also the former, are motoneurones to the myocardium. Both are probably sensitive, but to different degrees, to stretch or inflation of the heart, in the wall of which the ganglion lies (Bullock, Cohen & Maynard, 1954), and to the effects of the extrinsic inhibitor axon and the accelerator axons, of which Maynard (1954) reported there are two. The followers are integrative as indicated by the fact that their pattern of discharge is not the same as that of any antecedent cell.