Biomedical subjects

C C Turbes

Publications and source records attributed to C C Turbes.

At least 19 recordsLinked to original sources

PubMed1995

Cerebral cortical and hippocampal interactions and sequencing of perceptual information.

In these studies, recordings from cerebral cortical and limbic systems of cats are made of the dynamics of the electroencephalogram and evoked potentials. The hippocampus receives inputs from classification couples in global mappings and sends outputs back to the cortical regions that are originally responsible for input to the hippocampus. Because of the hippocampal loop structure operating parallel it appears to maintain an ordering of perceptual information in time of input from cortical networks. Repetitive stimuli are used to test the interaction patterns of evoked potentials in cortical and limbic regions.

Animals↗

PubMed1995

Hippocampal and cerebral cortical sequencing of cardiac activity--theta rhythm (4-10Hz).

Interaction of repetitive evoked potentials using visual and auditory stimuli has been show for the hippocampus and cerebral cortex. Selected components of the electrocardiogram (EKG) are used to stimulate certain nuclei of the amygdala. Extracellular unit potentials of the hippocampus shown repetitive activity. The micro-EEG of the cerebral cortex and dorsal hippocampus show rhythmic activity. In the hippocampus computer analysis of these analog signals show an increase of the theta rhythm related to the EKG (QRST) stimulation. Repetitive activity related to the heart rate (EKG) is evident in the cerebral cortex during stimulation.

Animals↗

PubMed1992

EEG dynamics. Brain processing of sensory and cognitive information.

The EEG oscillations and resonances before sensory stimulation are variable; unstable frequencies and amplitudes. The EEG time-coherency is variable and tends to be incoherent preceding sensory stimulation. The phase angle of the EEG between brain structures tends to be random and coherence between various brain structures is low before the stimulus. Following sensory stimulation, the frequency is stabilized and the amplitude is greatly enhanced. These responses are considered to be related to coupling of neural oscillators and nuclear resonance. The shift to a time-coherent state is considered to be related to a probabilistic harmonic oscillators. The phase angle after the stimulus is zero-phase in the brain rhythm channels in all brain structures as noted in the phase spectra. In the post stimulation period there is a change to high coherency between brain structures in the inherent frequencies of their brain rhythms. Internal evoked potentials shown in all the brain nuclei studied. All the frequencies in the evoked potential responses are dependent on spontaneous EEG activities prior to the stimulus.

Animals↗

PubMed1992

Brain states--brain rhythms--brain responses.

Oscillation and resonance of electrical activity of certain sets of neurons in the brain and spinal cord is an important factor in the organization of those properties of connectivity that must be tuned by function. Once connectivity has reached some degree of specificity important biological and chemical events must occur to stabilize synaptic inputs and localize excitable sites to particular areas of the cell surface. It has been proposed that intrinsic electroresponsiveness generates internal computational states that serves as a reference frame or context for incoming information. The intrinsic activity is proposed to be a part of the vectorial coordinate space that sensory and motor transformations occur in context of a particular functional state such as attention and expectation that can modify the relevance of a given sensory input. The most significant mechanism in generation of oscillation properties of the brain are the intrinsic properties of individual neurons. This concept presents a shift of emphasis from properties of circuits to properties of single neurons. Feedback circuits and synchronization of single oscillators into sets of coupled oscillators which in turn generates field potentials such as (EEG) and evoked response (ER).

Animals↗

PubMed1991

Studies of stereodynamic interaction of the EEG and auditory potentials of the limbic system and non-auditory frontal cortex.

These studies use 24 cats under non-anesthetic states. Electrodes are implanted, under appropriate anesthetic and stereotoxic procedures in non-auditory neocortical areas, nucleus accumbens, and certain nuclei of the amygdala complex. Auditory stimulation was done using the free field method with periodic tones at 2.0 KHz to 3.0 KHz at 80db. The auditory stimulation and recording was performed with hard wire and telemetry methods. The analog data is collected on FM tape and processed with minicomputer. Digital filtering, cross, coherence, phase, spectral and cycle time analyses are used on the analog data. In these studies, we have looked at the electroencephalogram (EEG) and the auditory evoked potentials (AEP) of cortical and subcortical regions using frequency and time domain methods. The analyses of the interaction of spatially distributed neuronal networks during EEG and AEP activity may give insights to topographical relations in the brain.

Animals↗

PubMed1991

Partial (coherence & correlation) estimates of brain autorhythmicity.

These experiments try to exhibit the interactions of the electrical activity of the microenvironment of a neuronal population spatially distant from the microenvironment of a different neuronal population. These experiments involve 18 cats with chronic electrodes surgically implanted into cerebral cortex, septal nuclei and amygdala. The Fast Fourier Transform (FFT) algorithm is done to process frequency domain data. In order to compare the phase relations between two channels, x(t) and y(T), use is often made of the coherence function. Computing partial coherence implies first eliminating from each two signals, that part which can be considered as being determined by, or predictable, on the basis of a third signal. It is assumed that there are three stochastic signals Y1, Y2, Y3. These variables can be considered as spectral components for a particular frequency. We assume that the correlations can be interpreted as square root of the coherence. For simplicity we use, in the partial correlations analyses.

Animals↗

PubMed1990

Autoregressive spectral filter studies on the sensorimotor rhythm EEG state variable.

These studies concern the EEG rhythms of the sensory motor cortex in cats. The cat generates a 12H to 16Hz rhythm related to the MU (Rolandic) rhythm in man. The behavioral state required to generate the rhythm in man and the cat requires complete immobility and alertness. The MU rhythm in man centers around 9Hz and in the cat at 12Hz to 16Hz. This rhythm is used in the biofeedback training for the treatment of intractable seizures in man. It has also been used (12 Hz to 16 Hz) experimentally in animals. It is necessary to enhance the MU rhythm and simultaneously depress the seizure activity. Our interest has been to detect and enhance the SMR rhythm (12 H to 16 Hz) in the cat. We found that when it is enhanced it also enhances the amplitude of auditory evoked potentials in other brain regions.

Algorithms↗

PubMed1990

Forty hertz (40Hz) and sensorimotor rhythms (SMR) as EEG state variables and related evoked potentials.

There is evidence that certain brain rhythms may signal the occurrence of different brain states. Support for this hypothesis may be provided by evidence that processing of information is changed during different brain states. The prestimulus period proceeding the auditory evoked potential (AEP) is converted to a power spectral estimate. These power spectra are used to sort for the AEP when certain power values for the (36-42Hz) and the (11-16Hz) are reached in the prestimulus period of the sensory motor cortex, nucleus accumbers and amygdala. Attempts are made to measure the performance of the 40Hz and SMR estimators. These studies are made in the cerebral cortical and subcortical regions in cats. In these studies D and L isomers of amphetamine are used to induce a chemical brain state changes. The AEP are selected in the amphetamine altered states based on the prestimulus auto spectra.

Analog-Digital Conversion↗

PubMed1989

Directionality of neural signals in central nervous system neural networks.

These studies are concerned with neuronal population theory of brain function. Neural networks the cerebral cortex and the limbic systems are investigated. We use coherence, partial coherence, phase and cycle time spectral analysis in these studies. The development of software for phase filtering has permitted us to analyze directionality of neural signal flow following coherence and partial coherence estimates. These estimates give an indication of the interaction between the brain regions studied. These data give further insights of the input and output status and the linear aspects of these interactions. Spontaneous and evoked potential analog data are analyzed to evaluate the physiological parameters of these interrelations.

Amygdala↗

PubMed1988