Peripheral Field Stimulation Research Articles

Central versus peripheral visual field stimulation results in timing differences in dorsal stream sources as measured with MEG

Small, achromatic circular sinusoids were presented in the central and peripheral visual fields to investigate dorsal visual stream activation. It was hypothesized that peripheral stimulation would lead to faster onset latencies, as well as preferentially activate dorsal stream visual areas relative to central field stimulation. Although both central and peripheral stimulation activated similar areas, the onset latencies of neuromagnetic sources in two dorsal stream areas were found to be significantly shorter for peripheral versus central field stimulation. The results suggest that information from central versus peripheral fields arrives in the higher-order visual areas via different routes.

Vigabatrin; its effect on the electrophysiology of vision.

Vigabatrin is known to induce visual field defects in approximately one third of patients treated with the drug. It is apparent from electrophysiological studies that the cause of this defect is at retinal level probably as a result of the build up of GABA. Studies of electrophysiological retinal parameters such as the EOG and photopic, scotopic and 30-Hz flicker ERG have revealed changes in Arden Index, photopic a and b wave latency and amplitude, changes in oscillatory potentials, and changes in latency and amplitude of the 30Hz response. However, many of these changes such as the Arden Index, oscillatory potentials, latency and amplitude of photopic b wave appear to be related to current anti-epileptic drug treatment rather than visual field defects. Certain parameters, particularly the amplitude of the 30-Hz flicker response, do appear to correlate with the severity of the field defect. Paediatric patients treated with the drug at age 9 years or below cannot reliably perform visual field perimetry. To identify these patients a special VEP H-Stimulus has been developed to produce separate responses from central and peripheral field stimulation by alternating at slightly separate rates. Forty-five healthy children between ages 3 and 10 years have been used to develop a normal database. This technique has a sensitivity of 75% and a specificity of 87.5% in identifying the field defect and may be used in children with epilepsy from age 3 upwards.

Differences in onset latencies of dorsal stream structures due to peripheral versus central visual field stimulation

Differences in onset latencies of dorsal stream structures due to peripheral versus central visual field stimulation

Objective visual field testing with functional magnetic resonance imaging

Purpose : To detect cortical retinotopy using the functional magnetic resonance imaging technique at clinical circumstances. Methods : Four normal volunteers were examined. Four experiments were performed on each subject: a ‘central-peripheral’ visual field stimulation and an ‘upper-lower’ visual field stimulation, both for right and left visual hemifields. The checkerboard stimuli, presented on a front projection screen, subtended 3 degrees of visual angle in height and 5 degrees in width. Sequential paradigms alternated rest phases with no checkerboard stimulation and stimulation phases. For the ‘central-peripheral’ visual field stimulation, the checkerboard was presented to either the central or peripheral visual field. During the ‘upper-lower’ visual field stimulation, the checkerboard was presented to either the upper or lower visual field. Results : The central visual field stimulation revealed a broad activated area in the contralateral occipital pole, whereas the peripheral visual field stimulation displayed a more anterior and narrower activated area. The ‘upper-lower’ visual field stimulation revealed broad activated areas covering the contralateral occipital pole. The upper visual field stimulation revealed the center of the cortical activation located inferiorly to lower visual field stimulation. Conclusion : Retinotopical eccentricity in the primary visual cortex is accurately detected using simple visual stimulations partially presented to the central-peripheral visual field. Upper visual field stimulation bordering the horizontal meridian could be differentiated from lower visual field stimulation in the associated visual cortex. This technique may help to evaluate the visual field.

Effects of attention on pattern-reversal visual evoked potentials: foveal field stimulation versus peripheral field stimulation.

The effects of foveal field attention on pattern reversal visual evoked potential (VEP) were investigated in thirteen normal subjects. Conventional monocular VEP was recorded during the three conditions of control, foveal concentration and reaction time task. Three patterns of checker-board, which were full field (radius, 0-9 degrees), peripheral field (2.5-9 degrees) and foveal field (0-2.5 degrees), were presented for the stimulation in each condition. The P100 and N145 amplitude of the peripheral field VEP were significantly smaller during the concentration and the reaction time task conditions that that in the control session, while the foveal field VEP amplitudes were enhanced in the concentration and reaction time tasks conditions. The full field VEP amplitudes were not significantly changed by the conditions. We concluded that the act of concentration to the foveal field or the task requiring attention to the foveal field, enhanced the VEP response to foveal field stimulation and suppressed the VEP to the peripheral field. A gating effect in area V1 was speculated, although extra-striate cortex might contribute.

Systemically administered cocaine alters stimulus-evoked responses of thalamic somatosensory neurons to perithreshold vibrissae stimulation

Previous studies have shown that systemically administered cocaine can transiently alter responses of primary somatosensory cortical neurons to threshold level stimulation of peripheral receptive fields. The goal of the present investigation was 2-fold: (1) characterize the effects of systemic cocaine on stimulus-evoked responses of the ventral posterior medial (VPM) thalamic neurons which relay somatosensory information to the cortex and (2) determine the time course and magnitude of changes in monoamine levels within the somatosensory thalamus following systemic administration of cocaine. Extracellularly recorded responses of single VPM thalamic neurons to whisker stimulation were monitored before and after cocaine administration in halothane anaesthetized rats. Each cell was first characterized by assessing its response profile to a range of perithreshold level deflections of the optimal whisker on the contralateral face. Drug effects on stimulus-response curves, response magnitude and latency were determined from quantitative analysis of spike train data. The results indicate that cocaine elicits a predictable augmentation or attenuation of the sensory response magnitude, with the direction of the change inversely related to the initial magnitude of the stimulus-evoked discharge. In addition, cocaine consistently reduced the response time of somatosensory thalamic neurons to peripheral receptive field stimulation. At the same dose and over the same time period, cocaine also produced marked elevation of norepinephrine and serotonin levels within the ventrobasal thalamus, as determined by in vivo microdialysis. These results suggest that cocaine-induced increases in norepinephrine and serotonin are responsible for drug-related modulation of the transfer of sensory signals through primary thalamocortical relay circuits.

Phasic activation of the locus coeruleus enhances responses of primary sensory cortical neurons to peripheral receptive field stimulation

In the present study we examined the effects of phasic activation of the nucleus locus coeruleus (LC) on transmission of somatosensory information to the rat cerebral cortex. The rationale for this investigation was based on earlier findings that local microiontophoretic application of the putative LC transmitter, norepinephrine (NE), had facilitating actions on cortical neuronal responses to excitatory and inhibitory synaptic stimuli and more recent microdialysis experiments that have demonstrated increases in cortical levels of NE following phasic or tonic activation of LC. Glass micropipets were used to record the extracellular activity of single neurons in the somatosensory cortex of halothane-anesthetized rats. Somatosensory afferent pathways were activated by threshold level mechanical stimulation of the glabrous skin on the contralateral forepaw. Poststimulus time histograms were used to quantitate cortical neuronal responses before and at various time intervals after preconditioning burst activation of the ipsilateral LC. Excitatory and postexcitatory inhibitory responses to forepaw stimulation were enhanced when preceded by phasic activation of LC at conditioning intervals of 200–500 ms. These effects were anatomically specific in that they were only observed upon stimulation of brainstem sites close to (>150 μm) or within LC and were pharmacologically specific in that they were not consistently observed in animals where the LC-NE system had been disrupted by 6-OHDA pretreatment. Overall, these data suggest that following phasic activation of the LC efferent system, the efficacy of signal transmission through sensory networks in mammalian brain is enhanced.

The effects of simultaneous central and peripheral field motion on the optokinetic response

The effects of central and peripheral retinal stimulation on the optokinetic response were examined using full-field, central field only, peripheral field only and simultaneous central and peripheral field motion. Stimulation of the central field in isolation produced similar responses to those obtained for full-field motion whereas peripheral field stimulation resulted in greatly reduced responses. Central field dominance was also evident during central and peripheral field motion in opposing directions. However with unidirectional, simultaneous central and peripheral stimulation the optokinetic response was determined not by the central stimulus but by whichever stimulus moved the slower.

Peripheral field stimulation affects foveal flicker, but not color, sensitivity

Human observers have different thresholds for flicker detection and color detection of a rapidly flickering spectral stimulus presented on a steady white background. A flickering surround, which did not overlap the stimulus or background, reduced flicker sensitivity but not color sensitivity for both monocular and binocular viewing. However, a flickering surround presented to one eye had no influence upon either color or flicker thresholds of the other eye.

Locomotion produced in mesencephalic cats by injections of putative transmitter substances and antagonists into the medial reticular formation and the pontomedullary locomotor strip

The purpose of this study was to determine the distribution of cells in the medial reticular formation (MRF) and the pontomedullary locomotor strip (PLS), which can induce locomotion when activated. Controlled microinjections of neuroactive substances (Goodchild et al., 1982) into the MRF or PLS were made in order to activate cell bodies in those areas. The ability of trigeminal receptive field stimulation to induce locomotion before and after drug infusion into the PLS was also assessed since the PLS and the spinal nucleus of the trigeminal nerve are similar in their anatomical distribution. Experiments were performed on precollicular-postmamillary decerebrate cats walking on a treadmill. Injections of glutamic acid (GA; 500 nmol) into the MRF produced locomotion that was antagonized by infusion of glutamic acid diethyl ester into the same spot. Decreases in the current threshold for locomotion produced by electrical stimulation of the MRF were observed when the MRF was infused with either GA (40-80 nmol), DL-homocysteic acid (DL-HCA; 200 nmol), or picrotoxin (PIC; 15 nmol). Injections of GA (100 nmol), DL-HCA (700 nmol), PIC (10-50 nmol), and substance P (2 nmol) into the PLS also produced locomotion. Locomotion produced by injections of PIC into the PLS was blocked by infusion of equal amounts of muscimol or GABA. Effective PLS injection sites were all confined to the trigeminal spinal nucleus or immediately ventral and medial to this in the adjacent lateral reticular formation. Trigeminal nerve peripheral field stimulation evoked locomotion after microinjection of PIC into the PLS, although this same facial stimulus was not effective prior to drug injection. We conclude that the MRF and PLS regions of the cat brain stem contain cells that produce locomotion when chemically stimulated, and we suggest that the PLS is closely related to or synonymous with the spinal nucleus of the trigeminal nerve. Furthermore, we suggest that stimulation of trigeminal afferents is analogous to stimulation of segmental afferent pathways in the production of locomotion (Sherrington, 1910; Jankowska et al., 1967; Afelt, 1970; Budakova, 1972; Grillner and Zangger, 1979).

Peripheral field stimulation suppresses flicker but not pattern detection in foveal targets.

This report examines the effects of peripheral visual stimulation on foveal target thresholds. The foveal targets were luminance-modulated sine-wave gratings (subtending 2° arc), presented with or without a phase-alternation of 1 Hz. The peripheral stimulus was a 20° black-white radial or linear, square-wave grating. The radial grating contained a 2° blank central area and appeared either at rest or in radial motion at 5°/sec. The linear grating contained either a 2° or an 8° central blank aperture and appeared either at rest or in oscillation by one-half cycle at 4 hz. Subjects always viewed the foveal target with their left eyes. The peripheral stimulus was presented to the left eye for monocular viewing but to the right eye for dichoptic viewing. For dichoptic viewing, the radial but not the linear grating increased the thresholds for counterphase but not stationary target gratings. For monocular viewing, both peripheral stimuli had threshold elevating effects on counterphase but not stationary targets. Results are discussed in terms of the binocular control of foveal monocular sensitivity.

Spatial contrast sensitivity: Effects of peripheral field stimulation during monocular and dichoptic viewing

This report examines whether a radial grating with a blank 2 deg central aperture viewed with one eye can affect contrast sensitivity for foveally-viewed, counterphasing or stationary, sine-wave gratings seen with the other eye. We find that the moving radial grating preferentially raises the threshold for the low spatial frequencies of the counterphasing but not the stationary foveal stimulus. These results closely parallel recent primate electrophysiological work which suggests that visual stimulation of the peripheral field with a moving radial grating can activate inhibitory corticofugal influences on lateral geniculate neurons. The current data are evaluated in terms of a model which suggests that the peripheral stimulus activates corticofugal mechanisms.

Effects of ablation of flocculus and paraflocculus of eye movements in primate.

1. Eye movements were recorded in four rhesus monkeys, before and after bilateral ablations of the flocculi and portions of the paraflocculi (“flocculectomy”). Animals were trained to fixate and follow targets so that pursuit, saccades, and vestibular and optokinetic nystagmus could be quantitated. 2. The vestibuloocular reflex (VOR) was mildly affected by flocculectomy. In darkness the VOR gain (eye velocity/head velocity) for steps of head velocity (normal range, 0.84-0.96) increased postoperatively in one monkey to 1.17, decreased in another to 0.62, and did not change significantly in the other two (0.96, 0.94). VOR phase lead at 0.05-Hz oscillation in darkness (normal range, O,O--LOO) increased in two monkeys by 12 and 9.5 O but did not change significantly in the others. 3. Visual suppression of inappropriate vestibular nystagmus was impaired. During oscillation at 0.25 Hz with a head-fixed visual scene, the average amount of attenuation of the VOR decreased from 5 1% preoperatively to 20% postoperatively. Visual suppression of caloric nystagmus was comparably affected. 4. Smooth tracking of small targets moving in space was impaired either with the head still (smooth pursuit) or moving (cancellation of the VOR by fixating a target rotating with the head). The average gain (gaze velocity/target velocity) in either case was about 0.65 (normal, 0.95-0.98). The pursuit deficit was less than that reported after total cerebellectomy, suggesting other cerebellar structures also participate in smooth tracking. 5. Optokinetic nystagmus (OKN) was present postoperatively but, in response to a constant-velocity stimulus, the initial slowphase velocity decreased by 50% and the rise time to a steady state nearly doubled. For stimuli belowr 6O”/s the average steady-state gain was only mildly diminished to 0.86 (normal, 0.98) and the time course of optokinetic afternystagmus (OKAN) in darkness was normal. The response to higher velocity optokinetic stimuli was impaired. These abnormalities can largely be attributed to the coexisting pursuit deficit although the protracted rise to a steady state suggests a change in the ability of the brain stem optokinetic system to handle large amounts of retinal slip. 6. Flocculectomized monkeys showed horizontally, gaze-paretic nystagmus with exponentially decaying centripetal drift (time constant, 1.56 s) and vertically, downbeat nystagmus with exponentially decaying (in three monkeys) or exponentially increasing (in one monkey) slow phases. All animals showed rebound nystagmus. These results implicate the flocculus and possibly the paraflocculus in the control of the time constant and stability of the brain stem oculomotor integrators. 7. Saccadic velocities and accuracy were normal but flocculectomized monkeys showed brief (40150 ms duration), approximately exponential, postsaccadic drift with amplitudes up to 15% of the size of the saccade. The eyes usually drifted in the same direction as the saccade but each monkey showed an idiosyncratic pattern depending on saccade direction and eye position. Postsaccadic drift may reflect a mismatch between the phasic (pulse) and tonic (step) innervational changes that create saccades.

Relationship between eye acceleration and retinal image velocity during foveal smooth pursuit in man and monkey.

Relationship between eye acceleration and retinal image velocity during foveal smooth pursuit in man and monkey.

Effect of altered central and peripheral visual field stimulation on correct recognition and visual evoked response.

Hemispheric asymmetry was assessed using combined electrophysiological (visual evoked response) and behavioral (percentage-correct-recognition) techniques. Right-handed, right-eyed, male undergraduates who viewed tachistoscopically exposed CVCs and random shapes in both central and peripheral visual fields were scored for their ability to recognize the stimuli correctly. Latency and amplitude of visual evoked responses were compared with correct recognition. Central and peripheral stimuli produced significant results. Superiority of the left hemisphere for verbal stimulus processing was supported. Small but consistent positive peak latencies of visual evoked responses also indicated language specialization of the left lobe. Results were interpreted as supporting hemispheric functional asymmetry. Additional findings of "cognitive masking" and marked reduction in intersubject variance in postive peak latencies of visual evoked responses by a central stimulus occurring at approximately 300 msec were also obtained. Mechanisms of iconic image storage, neuropsychological attentional theories, and differential hemispheric structural organization were discussed in interpreting results.

Neuronal depressant effects of diethylester derivatives of excitatory amino acids.

The effect of iontophoretically applied kainic acid diethylester (KDEE) on the firing rate of feline spinal interneurones was investigated and compared with the action of glutamic acid diethyles (GDEE) and aspartic acid diethylester (ADEE). All these esters reversibly reduced spontaneous neuronal firing and increased spike height, KDEE being the most active of this group. KDEE decreased response to glutamate, acetylcholine, and peripheral field stimulation, showing that its depressant action is not due to a selective antagonism of an excitatory putative transmitter.

Actions of microiontophoretically applied ibotenate on cat spinal interneurones.

Microiontophoretic applications of ibotenate, an amino acid analogue of glutamate, evoked biphasic responses from single dorsal horn interneurones of the cat spinal cord, i.e., an initial increase in the firing rate followed by a sustained depression of spontaneous firing. A reduced cell sensitivity to excitatory amino acids or peripheral field stimulation was also found during the ibotenate-induced depression. These effects were not produced by glutamate, quisqualate, or kainate, although occasional transient reductions of spontaneous cell firing were observed after application of glutamate. It is suggested that ibotenate might act on inhibitory as well as excitatory receptors of cat spinal interneurons.

Spatial and chromatic interactions in the lateral geniculate body of the rhesus monkey.

Spatial and chromatic interactions in the lateral geniculate body of the rhesus monkey.

RECEPTIVE FIELDS OF OPTIC TRACT AXONS AND LATERAL GENICULATE CELLS: PERIPHERAL EXTENT AND BARBITURATE SENSITIVITY.

RECEPTIVE FIELDS OF OPTIC TRACT AXONS AND LATERAL GENICULATE CELLS: PERIPHERAL EXTENT AND BARBITURATE SENSITIVITY.