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Biomedical subjects

W J Freeman

Publications and source records attributed to W J Freeman.

At least 55 records · Page 3Linked to original sources
PubMed1984

Periglomerular cell action on mitral cells in olfactory bulb shown by current source density analysis.

The sign of action of periglomerular (PG) cells on the apical dendrites of mitral cells in olfactory bulb glomeruli was investigated by constructing current source density (CSD) profiles from potentials evoked by primary olfactory nerve (PON) and lateral olfactory tract (LOT) stimulation. Evoked potentials were recorded and averaged from anesthetized rabbit simultaneously with a 1 X 16 array of electrodes positioned perpendicular to the bulbar surface. A one-dimensional CSD analysis with depth was made in the center of PON- and LOT-evoked potential activity. CSD was plotted vs depth for specific times during the average evoked potential (AEP): at the surface peaks of the first surface-negative wave (N1), the first surface-positive wave (P1), and the second surface-negative wave (N2). N1, P1 and N2 corresponded to excitation, dis-excitation (equivalent to inhibition), and dis-inhibition (re-excitation) of the granule cell population through mitral cell basal dendrites. The granule cells generated both PON and LOT oscillatory AEPs. When N1 and P1 profiles or P1 and N2 profiles were combined, the source and sink due to granule cell activity were minimized and another source-sink pair was revealed on PON but not LOT stimulation. PON-evoked N1 + P1 or P1 + N2 profiles showed a secondary souce-sink pair not present with LOT stimulation. The sink was located in the glomerular layer (GL) and outer plexiform layer (EPL) and the source in the inner EPL. It was concluded that long-lasting excitation of the mitral cells was taking place at the GL and GL/EPL border. This excitation was ascribed to concomitant PG cell activity, possibly in combination with prolonged monosynaptic PON excitation of the apical dendrites. The results support the occurrence of direct excitatory action of PG cells onto mitral cells.

Animals↗
PubMed1983

The physiological basis of mental images.

An important hypothesis in neurophysiology supposes that sensory information is encoded in spatial patterns of neural activity. A test of this hypothesis in rabbits reveals that the spatial pattern of encephalographic (EEG) activity of the olfactory bulb depends less on odor than on expectation of odor. Analysis of the structure and nonlinear dynamics of the olfactory system suggests that the EEG manifests a neural activity pattern that is an active filter corresponding to what ethologists call a "chemical search image." This first glimpse at the physical aspect of what may be a primitive form of mental image allows us to infer some of its properties. It is self-organized; input destabilizes the bulb, and the event runs a course that is shaped by the initial conditions, the sensory input, the chemical state of the bulb from centrifugal input, and the record of past input embedded in synaptic connections. The event is analog, but not an analog of input. Its intensity pattern exists in two dimensions but it is not a picture. Its bases in feedback and resonance make it connotative and ascriptive, not denotative or descriptive. The neural-mental image is an operator, not an operand. It gathers neurons by the millions into coherent activity and creates information, which it transmits to the next stage in the brain, thereby helping to shape behavior. It cannot be understood without reference to both what the subject does and what is done to it. Its function in the bulb is to regulate olfactory input with minimal and nonspecific centrifugal control.

Animals↗
PubMed1983

Conditioning of relative frequency of sniffing by rabbits to odors.

The sniff was identified by a brief episode of increased respiratory rate, usually with a well-defined time of onset. It was detected against the background of respiratory activity in rabbits simply, reliably, and noninvasively by statistical evaluation of digitized pneumograph records. The basal rate of exploratory sniffing was controlled by familiarization. Upon conditioning to olfactory cues, the rate of sniffing for CS+ increased sharply above the basal rate during the first 10 trials and was maintained at high levels by continued reinforcement. During extinction with discrimination between olfactory cues, the rate for CS- fell sharply at first and then more slowly toward the basal rate. With pseudoconditioning, the rabbits responded to an unpaired odor after several sessions; the rates of response acquisition and extinction and the maintained level of responding were lower than with a paired odor in classical delayed conditioning, and the response was not discriminative in respect to another novel odor given during extinction. The sniff displayed a prominent sensory bias for olfactory cues. The relative frequencies of sniffing and respiratory slowing were measured as conditioned responses by screening procedures with a small computer.

Animals↗
PubMed1980

Effects of carnosine on olfactory bulb EEG, evoked potentials and DC potentials.

Carnosine is a dipeptide found in great quantities in the primary olfactory nerve and has been suggested to be the neurotransmitter of the olfactory receptor axons. The aim of the present study was to describe some of its electrophysiological actions in the olfactory bulb (OB) of rabbits under anesthesia. Carnosine as a 10% solution in amounts of 2-5 microliter was injected to the OB at the level of the glomerular layer by means of a pipette attached to a Hamilton syringe. Average evoked potentials (AEPs) on the stimulation of the lateral olfactory tract (LOT-AEP), electroencephalographic (EEG) activity and slow potential (DC) recordings were obtained. The LOT-AEPs were analyzed by fitting damped sine waves to them. The parameters of amplitude, frequency, decay rate, phase and rise rate were measured and statistically compared to the values obtained prior to the carnosine injection. An increase in frequency and decreases in the phase and the decay rate of the AEP were found. Carnosine also produced a sustained oscillation in the EEG and a surface negative, deep positive shift in the DC recording. The changes were maximal within the first minute after injection and lasted 2-7 min. Tyrodes' solution, which was used as the carnosine vehicle, did not produce any changes, nor did beta-alanine, which is one of the constituents of carnosine, at equivalent osmotic concentrations. It is concluded that carnosine has an excitatory action on the mitral/tufted cells, and that this effect is obscured by a secondary increase in granule cell (inhibitory) activity.

Animals↗
PubMed1980

Frequency analysis of olfactory system EEG in cat, rabbit, and rat.

EEG activity in the 35--85 c/sec range has been reported from the rhinencephalon of numerous species of homeotherms, and from numerous parts of the forebrain in carnivores and primates, including man. Unimodal distributions of frequencies within this range for each of 3 species (cat, rat and rabbit) are reported here with proportionality between means and variances. Theoretical analysis has shown that the basis for this oscillatory activity lies in the feedback synaptic interactions of assemblies of excitatory and inhibitory neurons, and that there is a neural basis for frequency convergence and high amplitude near 40 c/sec. Given the synaptic mechanisms, the unimodal spectral distributions, and the widespread occurrence of EEG activity in this range, it clearly represents a unique and identifiable form of brain activity.

Animals↗
PubMed1979

EEG analysis gives model of neuronal template-matching mechanism for sensory search with olfactory bulb.

The spatial pattern of EEG activity at the surface of the olfactory bulb tends to be invariant with respect to input and to change to a new pattern whenever an animal is trained to expect or search for a particular odor. It is postulated here that the spatial EEG pattern is dependent on a neural template for that odor that is formed during training. This hypothesis is expressed in the form of a model consisting of an array of interconnected elements (1 X 10 or 6 X 6). Each element represents 2 excitatory and 2 inhibitory subsets of neurons with 3 types of internal feedback: negative, mutually excitatory, and mutually inhibitory. The elements are interconnected only by mutual excitation and mutual inhibition. Each neural subset is represented by a nonlinear differential equation; the connections are represented by modifiable coupling coefficients. With appropriate values of the time, coupling, and gain coefficients, and with input that is modelled on olfactory input, the set of 40 or 144 equations gives output that simulates the time and space patterns of the EEG. In the naive state the coefficients are uniform. A template is formed by giving input to selected elements, cross-correlating the outputs, and weighting the mutually excitatory coupling coefficient between each pair of elements by the corresponding correlation coefficient. When a template has been formed, input to nontemplate elements is treated as noise. Optionally a matched filter is made to simulate habituation by reducing the synaptic gain coefficients of those excitatory subsets that receive the noise. The model is tested by giving input to nontemplate elements and to none, part or all of the template elements. There are two outputs of the model. One is the spatial pattern Vj of the root mean square (rms) amplitudes of the individual outputs v(j, t) of the elements. The other output is the rms amplitude Erms of the ensemble average E(t) over v(j, t). The results show that Vj depends on the template and is relatively insensitive to input, whether or not input is given to template elements. However, Erms increases in proportion to the number of "hits" on the template. If the number of elements receiving noise does not exceed the number of elements in a template, or if the noise is matched with a habituation filter, then Erms rises above the noise level for a "hit" on any one or more template elements irrespective of location or combination. Vj conforms to the performance of the surface EEG. Erms is not yet accessible to physiological measurement.

Animals↗
PubMed1979

Nonlinear dynamics of paleocortex manifested in the olfactory EEG.

The olfactory bulb is the first central component in a highly sensitive yet markedly stable sensory system. It receives a surge of receptor activity with each inspiration and transmits output as a brief burst of oscillatory activity that is most clearly seen in the EEG. These properties together with the known anatomy and physiology of the bulb are used as design criteria to synthesize, evaluate and solve a set of nonlinear differential equations that represent lumped bulbar dynamics. According to the model bulbar processing is in two stages. In the outer layers the interneurons perform the operations of input range compression, integration, clipping, holding, and bias control. In the inner layers the input surge is converted to a burst, which is transmitted by the mitral cells as a pulse density wave. The phase, frequency duration and amplitude of the wave convey information centrally about both the input and the state of the system. The model suffices to replicate the forms of the EEG burst; the pulse probability distributions conditional on the EEG; the waveforms of averaged evoked potentials (AEPs) and post stimulus time (PST) histograms from the bulb and cortex; and the changes in waveform induced by behavioral control of attentiveness and habituation. It is inferred that with selective attention there is a permanent change in the strength of mutually excitatory connections among excitatory neurons, and that with habituation there is a reversible change in the effectiveness of excitatory synapses. The limitations and deficiencies of the model and the need for centrifugal controls of bulbocortical function are discussed.

Action Potentials↗
PubMed1978

Models of the dynamics of neural populations.

Three requirements are posed for constructing models to simulate EEG dynamics. The element of the model should be an interactive ensemble of neurons and not single neurons. The observations must be statistical, such as EEG waves and averages of unit activity over time and over local neighborhoods containing neural subsets. The state variables and operations of the model must be clearly related to behavioral functions such as sensory reception and perception. A model is presented that exemplifies these requirements. Its key feature is the dependence of its levels of interaction on the level of its input, so that with each burst of input the model switches from an equilibrium state to a limit cycle state. A mechanism is described for coding sensory input into the spatial modulation of the limit cycle activity viewed as a carrier. It is suggested that sensory recepts and percepts exist at different hierarchical levels in the brain, recepts at the level of single neurones, and percepts at the level of neural ensembles, the latter being possibly manifested in the EEG.

Animals↗