An analysis of primary response of visual cortex to optic nerve stimulation in cats

Utilization of Discretization method on the diagnosis of optic nerve disease

The optic nerve disease is an important disease that appears commonly in public. In this paper, we propose a hybrid diagnostic system based on discretization (quantization) method and classification algorithms including C4.5 decision tree classifier, artificial neural network (ANN), and least square support vector machine (LSSVM) to diagnose the optic nerve disease from Visual Evoked Potential (VEP) signals with discrete values. The aim of this paper is to investigate the effect of Discretization method on the classification of optic nerve disease. Since the VEP signals are non-linearly-separable, low classification accuracy can be obtained by classifier algorithms. In order to overcome this problem, we have used the Discretization method as data pre-processing. The proposed method consists of two phases: (i) quantization of VEP signals using Discretization method, and (ii) diagnosis of discretized VEP signals using classification algorithms including C4.5 decision tree classifier, ANN, and LSSVM. The classification accuracies obtained by these hybrid methods (combination of C4.5 decision tree classifier-quantization method, combination of ANN-quantization method, and combination of LSSVM-quantization method) with and without quantization strategy are 84.6-96.92%, 94.20-96.76%, and 73.44-100%, respectively. As can be seen from these results, the best model used to classify the optic nerve disease from VEP signals is obtained for the combination of LSSVM classifier and quantization strategy. The obtained results denote that the proposed method can make an effective interpretation and point out the ability of design of a new intelligent assistance diagnosis system.

Effect of interruption of the visual pathway on the response to geniculate stimulation

Optic nerve section or destruction of the lateral geniculate nucleus increased the amplitude and elevated the recovery cycle of the cortical response to lateral geniculate radiation stimulation in cats. The lesions may have acted by eliminating tonic inhibitory or occlusive volleys originating in the retina, or both.

The effects of selective glutamate receptor antagonists on synchronized firing bursts in layer III of rat visual cortex

In the rat visual cortex in vitro, single-shock stimulations applied to the border between layer VI and the white matter evoke synchronized burst-firing by units in layer III. We have examined the effects of glutamate receptor antagonists on this activity, with antagonists applied via the bath to allow correlation of effects with concentrations. All synaptically driven components (recorded extracellularly as field potential 'S2' spikes, dipoles 'W1' and 'W2', and coinciding single-unit spikes) were inhibited by greater than 90% in 1.0 mM kynurenic acid and in 3 or 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, which selectively blocks AMPA/kainate receptors). S2 spike amplitudes were reduced by half in 0.7 microM CNQX. 2-Amino-5-phosphonovalerate (APV), a specific blocker of NMDA receptors, did not prevent S2 spike burst or horizontal spread of bursting within layer III. However, APV reduced the duration of synchronized bursts and the slower potentials which followed. In Mg(2+)-free medium, new components appeared which were APV-sensitive: (1) low amplitude spikes, distributed spatially like S2 spike, but recurring more slowly, and (2) slow potentials, distributed spatially like W1 and W2 potentials, but lasting for hundreds of milliseconds. The amplitudes of these spikes were reduced by half in 3 microM D-APV. Our data imply that: (1) glutamate receptors play a major role in mediating local, excitatory neurotransmission in the supragranular layers of neocortex, with NMDA and AMPA/kainate subtypes each subserving somewhat different functions; (2) AMPA/kainate receptors mediate rapid excitatory transmission between layer III neurons, responsible for driving the first 15 ms of synchronized bursts; (3) currents gated by NMDA receptors determine the duration of coherent firing bursts, and drive asynchronous neuronal firing following bursts; and (4) under conditions which circumvent block by extracellular Mg2+, activation of NMDA receptors greatly enhances and prolongs the response to single-shock stimulations. In vivo, activation of layer III neurons is likely to depend significantly upon currents gated by NMDA receptors whenever repetitively firing excitatory inputs summed over several tens of milliseconds provide enough depolarization to lift block by extracellular Mg2+.

Laminar analysis of the origin of the various components of evoked potentials in slices of rat sensorimotor cortex

In slices of rat sensorimotor cortex, extracellular field potentials evoked by electrical stimulation of the white matter were recorded at various cortical depths. In order to determine the nature of the various components, experiments were performed in 3 situations: in a control perfusion medium, in a solution in which calcium ions had been replaced by magnesium ions to block synaptic transmission, and in cortices in which the pyramidal neurons of layer V had been previously induced to degenerate. In the control situation, the response at or near the surface was a positive-negative wave. From a depth of about 150 microns downwards, the evoked response consisted usually of 6 successive components, 3 positive-going, P1, P3 and P6 and 3 negative-going, N2, N4 and N5. P1 and N4 were apparent in superficial layers only. The amplitude of the remaining waves was variable in the cortex but all diminished near the white matter. The early part of the surface positive wave arises from a non-synaptic activation of superficial elements, probably apical dendrites. The late part of the surface positive wave and the negative wave are due to the synaptic activation of neurons located probably in layer III. The large negative wave N2 represents principally the antidromic activation of cell bodies and possibly of proximal dendrites of neurons situated in layers III, IV and V, though the compound action potentials of afferent and efferent fibers may contribute to a reduced part to its generation. The late components N4 to P6 are post-synaptic responses. The negative component N5, the amplitude of which is largest in layers III and IV, represents excitatory responses of neurons located at various depths in the cortex. The nature of the positive component P6 is less clear, although the underlying mechanism might be inhibitory synaptic potentials.

The effect of dark adaptation on the responses of cat retinal ganglion cells to eyeball deformation

Eyeball deformation in total darkness leads to an activation of on-center ganglion cells and an inhibition of off-center ganglion cells. After "deformation off" most on-center ganglion cell activity decreased slowly to the normal spontaneous dark level, while in off-center ganglion cells some returned according to an exponential function to normal dark activity, while others had a transient postinhibitory activation period. In general, the response type of latency class I and latency class II neurons was the same. Dark adaptation of 30-45 min duration only changed this neuronal response pattern slightly, if at all. A detailed statistical analysis is provided for the four classes of retinal ganglion cells recorded: latency class I on-center and off-center neurons and latency class II on-center and off-center neurons. The missing effects of dark adaptation on neuronal responses evoked by eyeball deformation are explained by three possible models. The more plausible one assumes that horizontal cells are depolarized by retinal stretch. Their interaction with cone on-bipolars or cone off-bipolars is fairly independent of photoreceptor adaptation or transmitter release at the cone pedicles and is still effective when all molecular receptor sites at cone/bipolar cell synapses are occupied during scotopic states of dark adaptation. In psychophysical experiments (two subjects), as in the neuronal responses, we also could not find any indication that the "pressure phosphenes" evoked by lateral eyeball indentation are altered during dark adaptation.

Statistical argument for a presynaptic origin of the second positive component of somesthetic primary cortex evoked potential elicited by central afferent stimulation

The positive components 1 and 2 of the averaged field response induced in the somesthetic S1 cortex by submaximal stimulation of cortical radiation and supramaximal stimulation of lemniscus medialis showed non-existent amplitude variability whereas the dispersion was significant for components 3, 4 and 5. The same stimulus delivered at a short intershock interval only induced waves 1 and 2 without any amplitude variability, the three following ones being under complete refractoriness. These results suggest a presynaptic origin of component 2.

The neural circuitry of the neocortex examined in the in vitro brain slice preparation

The in vitro brain slice technique has been applied to the study of the neocortex. Cortical blocks were removed from adult rats deeply anesthesized with halothane, sectioned coronally at 400-700 micrometer, and placed in a brain slice chamber. Cortical slices typically showed spontaneous and evoked potential activity and normal histology for 8 h or longer. Single units and evoked potential recordings were made from different layers of the cortex using micropipettes. The evoked potentials to electrical stimulation of differing intensity, frequency, and from different cortical layers were analyzed. Evoked potential from all but the most superficial layers of the cortex showed a characteristic 6-component response to stimulation of nearby white matter. This evoked potential closely resembled cortical responses recorded in vivo by other investigators following afferent stimulation. The response amplitude of all components increased as stimulus intensity was raised. Radial movement of the recording electrode showed that components 1-3 had their largest amplitudes in the deepest cortical layers, component 4 reached its greatest amplitude and shortest latency in layer IV, and components 5 and 6 reached their greatest amplitudes in layers IV to II. The frequency following for various components was measured showing greater decline in amplitude for components 4-6 than 1-3. This, together with the results of previous investigators, suggests that the first 3 components represent afferent fiber input, while component 4 represents the first cortical response (layer IV). Components 5 and 6 represent later, additional cortical responses. Further support for the intracortical origin of component 4 was provided by lateral intracortical stimulation within layer IV, giving an evoked potential composed mostly of component 4. With lateral movement of the recording electrode in layer IV the evoked potential disappeared in under 1 mm, suggesting a fairly restricted afferent input to the cortex. The present results encourage the use of the cortical brain slice preparation as an appropriate model system in which to study cortical neural circuitry.

Enhancement of cortical evoked potentials by high atmospheric pressures of helium

Adult guinea pigs with electrodes chronically implanted in the optic chiasm (OC(, lateral geniculate nucleus (LGN), and visual cortex (CX) were compressed at 1 bar/min to 120 bars pressure in helium-oxygen. Body temperature was controlled to within +/- 1 degree C, CO2 was removed by a soda-lime absorbent. Electrical stimuli (50 microA, 0.05 msec) were delivered to the OC at 9.6/sec at 10 bar intervals, with pressure held constant. Pressure caused only negligible changes inthe amplitudes of pre- and postsynaptic components of potentials in the LGN. Amplitudes of evoked potentials in the CX increased approximately linearly with pressure, reaching values of up to 300% above normobaric. Latencies did not change independently of temperature. Excitability of nerve fibers changed very little, but intracortical synaptic transmission was substantially enhanced. Differences in the effects of elevated helium pressure at the LGN and CX may be attributed to differences in organization of local circuits.

Maintained activity, excitation and inhibition of lateral geniculate neurons after monocular deafferentation in the adult cat

Monocular deafferentation of the lateral geniculate nucleus (LGN) was accomplished by photocoagulation of the retinal vessels and the optic disc of one eye. Single cells with normal excitatory innervation from the intact eye (N-cells) and deafferented (D-) cells were recorded extracellularly with glass micropipettes from layers A and A1 of the LGN 10 days and 10 weeks after visual deafferentation. The maintained activity of D-cells was severely reduced after 10 days but had recovered significantly after 10 weeks. Different interspike interval distributions indicated a change in the main input source for the reactivated cells after 10 weeks. Stimulation of the intact retina with diffuse, high-intensity light flashes revealed missing or very small responses in the acutely deafferented cells. A still weak influence of the non-dominant eye on the deafferented cells after 10 days developed after 10 weeks into a biphasic response with an initial inhibitory period followed by a post-inhibitory exciation. Electrical stimulation of the optic chiasm revealed an increased inhibition during chronic deafferentation. Excitation following this inhibitory period was rare after 10 days but occurred frequently after 10 weeks. An enhanced excitability following stimulation of the visual cortex and the mesencephalic reticular formation was also observed after 10 weeks of deafferentation. An increased efficiency of all remaining inputs to the visually deafferented cells is concluded from the augmented inhibition and non-retinal excitation.

Visual evoked response and behavioral correlates of plasma methadone concentrations in cats

Twelve cats were implanted with cortical and depth electrodes. After they recovered from the operation, visual evoked responses (VERs) were recorded at 20 min following saline and methadone (0.5, 1, 2, 3, 4 mg/kg) administered IP in a semi-random order to each cat. Four other cats were similarly drugged and plasma was obtained for radioimmunoassay of methadone content. At the three lowest dose levels behavioral excitation and salivation were evident in some cats, while their VER configuration remained essentially unaltered and plasma methadone was barely measurable. Following the 3 and 4 mg/kg doses plasma methadone concentration increased dramatically, behavioral excitation and salivation were evident in most cats and VERs were reliably altered. The VER alterations, consisting of amplitude attenuation and a decrease in some latencies, were restricted to secondary VER components occurring between 50 and 100 msec despite the animals' extreme behavioral excitation. These results suggest that the reticular formation is not a principal site of the drug's effect.

Visual evoked potentials during the development of a spiking cobalt focus in rat neocortex

Averaged visual evoked potentials recorded from three electrode placements in visual cortex in response to single and paired light flashes were acquired from rats with epileptogenic cobalt implants or with stainless-steel control implants. Evoked potentials acquired after computer-detected epileptic spikes were also recorded from rats in the cobalt group. Epileptic spiking began between the 6th and 9th postoperative days and flashes then began to evoke epileptic spikes. Excitability cycles were assessed. On the day showing the maximum rate of spiking, excitability at the site of the cobalt was markedly reduced following flash-triggered or spontaneous epileptic spikes in almost all cases. By contrast, the electrode placement in contralateral homotopic cortex showed nearly normal excitability despite the presence of large amplitude epileptiform spikes and sharp waves projected from the site of the cobalt. The results are discussed with reference to other experimental findings.

Intracellular postsynaptic potentials of cat lateral geniculate cells and the effects of degeneration of the optic terminals

(1) The synaptic signal transmission was studied in the lateral geniculate nucleus (LGN) during the late phase of degeneration, 50-80 h after light coagulation of the optic disc and the retinal vessels of one eye. Postsynaptic potentials and action potentials were intracellularly recorded from normal LGN principal cells (N-cells) and cells with degenerating optic terminals (D-cells). EPSPs and postsynaptic action potentials were elicited by electrical stimulation of the optic tract. Two neuronal classes (I and II) were characterized according to their response latency to optic tract stimuli. (2) Spontaneous small EPSPs and slow changes of the membrane potential were found in D-cells and the EPSP-IPSP pattern normally present in N-cells was absent. (3) The responses to optic tract stimuli applied at low stimulus frequencies (less than 5 stimuli/sec) were identical in D-cells and N-cells. (4) At higher stimulus frequencies (greater than 50 stimuli/sec), the EPSP amplitude was, on average, significantly smaller in D-cells than in N-cells. (5) At frequencies above 50 stimuli/sec, the fluctuation of the EPSP amplitudes and the latency scattering of postsynaptic action potentials were larger in D-cells than in N-cells. (6) The slope of the rising phase of the EPSPs increased slightly in N-cells and decreased in D-cells when the stimulus frequency was raised from 5/sec to 100/sec (class I cells). (7) The decay time constant of the EPSP, the latency of the onset and the peak amplitude of EPSPs did not change during degeneration. (8) The hypothesis put forward to account for the results is that the amount of transmitter released by each action potential in degenerating terminals is reduced, but its variability is increased. This is probably caused by a reduction in both the transmitter reserve and the transmitter resynthesis, and also by a larger fluctuation of the size of transmitter quanta.