BRAIN AND EYE AS POTENTIAL TARGETS FOR IONIZING RADIATION IMPACT. PART III / FEATURES MORPHOMETRIC RETINAL PARAMETERS, AMPLITUDE AND LATENCY COMPONENTS OF VISUAL EVOKED POTENTIAL IN RADIATION EXPOSED IN UTERO. / GOLOVNYI MOZOK TA ORGAN ZORU IaK POTENTsIINI MIShENI DLIa VPLYVU IONIZUIuChOGO VYPROMINIuVANNIa: ChASTYNA III ­ OSOBLYVOSTI MORFOMETRYChNYKh PARAMETRIV SITChASTOÏ OBOLONKY TA AMPLITUDA I LATENTNIST' KOMPONENTIV ZOROVYKh VYKLYKANYKh POTENTsIALIV U OPROMINENYKh VNUTRIShN'OUTROBNO OSIB.

One of the current problems of modern radiobiology is determine the characteristics of the manifestation of radiation-induced effects not only at different dose loads, but also at different stages of development of the organism. In previous reports, we have summarized available evidence that at certain ages there is a comparative acceleration of radiation-induced pathological changes in the eye and brain, and the study and assessment of the risk of possible ophthalmic and neurological pathology in remote periods after contamination of radioactive areas. Data of irradiated in utero individuals are possible on the basis of observation of the state of the visual analyzer in persons who underwent intrauterine irradiation in 1986. Therefore, a parallel study of retinal morphometric parameters, amplitude and latency of components of evoked visual potentials in irradiated in utero individuals was performed. OBJECTIVE: to evaluate the retinal morphometric parameters, amplitude and latency components of the evoked visual potentials in intrauterine irradiated persons. MATERIALS AND METHODS: The results of surveys of 16 people irradiated in utero in the aftermath of the Chornobyl disaster were used; the comparison group were residents of Kyiv of the corresponding age (25 people). Optical coherence tomography was performed on a Cirrus HD-OCT, Macular Cube 512x128 study technique was used. At the same time, the study of visual evoked potentials on the inverted pattern was performed, and occipital leads wereanalyzed. Visual evoked potentials were recorded on a reversible chess pattern (VEP) - an electrophysiological test, which is a visual response to a sharp change in image contrast when presenting a reversible image of a chessboard. RESULTS: In those irradiated in utero at the age of 22-25 years, there was a probable increase in retinal thickness in the fovea, there was a tendency to increase the thickness of the retina in the areas around the fovea. When recording visual evoked potentials on a reversible chess pattern in this group, there was a tendency to decrease the amplitudes of components (N75, P100, N145, P200) in the right and left parieto-occipital areas and asymmetric changes in latency of these components. CONCLUSIONS: Early changes of fovea recorded in OCT and decreasing amplitudes of components of visual evoked potentials on the reversible chess pattern at the age of 22 25 years may indicate a risk of development in patients irradiated in utero, early age-related macular degeneration, as well as increased risk and increased risk structures of the visual analyzer.

The effect of 4.5 G (LTE Advanced-Pro network) mobile phone radiation on the optic nerve.

PURPOSE: Rapid development in mobile phone technologies increase the average mobile phone usage duration. This increase also triggers exposure to radiofrequency radiation (RF), which is a risk factor for the health. In this study, it was aimed to investigate the effect of mobile phone working with LTE-Advanced Pro (4.5 G) mobile network on the optic nerve, which is responsible for the transmission of visual information. MATERIAL AND METHODS: Thirty-two rats divided into two groups as control (no RF, sham exposure) and experimental (RF exposure using a mobile phone with LTE-Advanced Pro network; 2 hours/day, 6 weeks). The visual evoked potential (VEP) was recorded and determined amplitudes and latencies of VEP waves. Optic nerve malondialdehyde level, catalase and superoxide dismutase activities were determined. Furthermore, ultrastructural and morphometric changes of optic nerve were evaluated. RESULTS: In VEP recordings, the mean VEP amplitudes of experimental group were significantly lower than control group. In ultrastructural evaluation, myelinated nerve fibres and glial cells were observed in normal histologic appearance both in sham and experimental group. However, by performing morphometric analysis, in the experimental group, axonal diameter and myelin thickness were shown to be lower and the G-ratio was higher than in the sham group. In the experimental group, malondialdehyde level was significantly higher and superoxide dismutase and catalase activities were significantly lower than sham group. There was a high correlation between VEP wave amplitudes and oxidative stress markers. CONCLUSION: Findings obtained in this study support optic nerve damage. These results point out an important risk that may decrease the quality of life.

Does acute radio-frequency electromagnetic field exposure affect visual event-related potentials in healthy adults?

OBJECTIVE: To use improved methods to address the question of whether acute exposure to radio-frequency (RF) electromagnetic fields (RF-EMF) affects early (80-200 ms) sensory and later (180-600 ms) cognitive processes as indexed by event-related potentials (ERPs). METHODS: Thirty-six healthy subjects completed a visual discrimination task during concurrent exposure to a Global System for Mobile Communications (GSM)-like, 920 MHz signal with peak-spatial specific absorption rate for 10 g of tissue of 0 W/kg of body mass (Sham), 1 W/kg (Low RF) and 2 W/kg (High RF). A fully randomised, counterbalanced, double-blind design was used. RESULTS: P1 amplitude was reduced (p = .02) and anterior N1 latency was increased (p = .04) during Exposure compared to Sham. There were no effects on any other ERP latencies or amplitudes. CONCLUSIONS: RF-EMF exposure may affect early perceptual (P1) and preparatory motor (anterior N1) processes. However, only two ERP indices, out of 56 comparisons, were observed to differ between RF-EMF exposure and Sham, suggesting that these observations may be due to chance. SIGNIFICANCE: These observations are consistent with previous findings that RF-EMF exposure has no reliable impact on cognition (e.g., accuracy and response speed).

(Re)-wiring a brain with light: Clinical and visual processing findings after application of specific coloured glasses in patients with symptoms of a visual processing disorder (CVPD): Challenge of a possible new perspective?

The present investigation examined whether changes of electrophysiological late event related potential pattern could be used to reflect clinical changes from therapeutic intervention with coloured glasses in a group of patients with symptoms of central visual processing disorder. Subjects consisted of 13 patients with average age 16years (range 6-51years) with attention problems and learning disability, respectively. These patients were provided with specified coloured glasses which were required to be used during day time. Results indicated that specified coloured glasses significantly improved attention performance. Furthermore electrophysiological parameters revealed a significant change in the late event related potential distribution pattern (latency, amplitudes). This reflects a synchronization of together firing wired neural assemblies responsible for visual processing, suggesting an accelerated neuromaturation process when using coloured glasses. Our results suggest that the visual event related potentials measures are sensitive to changes in clinical development of patients with deficits of visual processing wearing appropriate coloured glasses. It will be discussed whether such a device might be useful for a clinical improvement of distraction symptoms caused by visual processing deficits. A model is presented explaining these effects by inducing the respiratory chain of the mitochondria such increasing the low energy levels of ATP of our patients.

Optogenetic Vision Restoration Using Rhodopsin for Enhanced Sensitivity.

Retinal disease is one of the most active areas of gene therapy, with clinical trials ongoing in the United States for five diseases. There are currently no treatments for patients with late-stage disease in which photoreceptors have been lost. Optogenetic gene therapies are in development, but, to date, have suffered from the low light sensitivity of microbial opsins, such as channelrhodopsin and halorhodopsin, and azobenzene-based photoswitches. Several groups have shown that photoreceptive G-protein-coupled receptors (GPCRs) can be expressed heterologously, and photoactivate endogenous Gi/o signaling. We hypothesized such a GPCR could increase sensitivity due to endogenous signal amplification. We targeted vertebrate rhodopsin to retinal ON-bipolar cells of blind rd1 mice and observed restoration of: (i) light responses in retinal explants, (ii) visually-evoked potentials in visual cortex in vivo, and (iii) two forms of visually-guided behavior: innate light avoidance and discrimination of temporal light patterns in the context of fear conditioning. Importantly, both the light responses of the retinal explants and the visually-guided behavior occurred reliably at light levels that were two to three orders of magnitude dimmer than required for channelrhodopsin. Thus, gene therapy with native light-gated GPCRs presents a novel approach to impart light sensitivity for visual restoration in a useful range of illumination.

Electrophysiological monitoring in patients with tumors of the skull base treated by carbon-12 radiation therapy.

PURPOSE: To report the results of short-term electrophysiologic monitoring of patients undergoing (12)C therapy for the treatment of skull chordomas and chondrosarcomas unsuitable for radical surgery. METHODS AND MATERIALS: Conventional electroencephalogram (EEG) and retinal and cortical electrophysiologic responses to contrast stimuli were recorded from 30 patients undergoing carbon ion radiation therapy, within a few hours before the first treatment and after completion of therapy. Methodologies and procedures were compliant with the guidelines of the International Federation for Clinical Neurophysiology and International Society for Clinical Electrophysiology of Vision. RESULTS: At baseline, clinical signs were reported in 56.6% of subjects. Electrophysiologic test results were abnormal in 76.7% (EEG), 78.6% (cortical evoked potentials), and 92.8% (electroretinogram) of cases, without correlation with neurologic signs, tumor location, or therapy plan. Results on EEG, but not electroretinograms and cortical responses, were more often abnormal in patients with reported clinical signs. Abnormal EEG results and retinal/cortical responses improved after therapy in 40% (EEG), 62.5% (cortical potentials), and 70% (electroretinogram) of cases. Results on EEG worsened after therapy in one-third of patients whose recordings were normal at baseline. CONCLUSIONS: The percentages of subjects whose EEG results improved or worsened after therapy and the improvement of retinal/cortical responses in the majority of patients are indicative of a limited or negligible (and possibly transient) acute central nervous system toxicity of carbon ion therapy, with a significant beneficial effect on the visual pathways. Research on large samples would validate electrophysiologic procedures as a possible independent test for central nervous system toxicity and allow investigation of the correlation with clinical signs; repeated testing over time after therapy would demonstrate, and may help predict, possible late toxicity.

Visual efference in Limulus: in vitro temperature-dependent neuromodulation of photoreceptor potential timing by octopamine and substance P.

Efferents from the brain of Limulus course toward its lateral eye and release octopamine and substance P into it. These neurotransmitters have previously been found to act as neuromodulators in this visual system by altering the size of its responses to light. We report here that both also modulate the timing of the receptor potentials (RPs) evoked by brief light flashes and that these timing effects are temperature dependent. Specifically: We extend our previous report that octopamine prolongs ambient RPs in a categorical fashion and here demonstrate that it does the same at colder temperatures. Categorical means that a given RP is either clearly prolonged in a dramatic fashion or its duration is otherwise unremarkable. Octopamine also accelerates the onsets of RPs when they are evoked by weak flashes under cold temperatures. Contrariwise, substance P accelerates RPs at all temperatures and this acceleration dramatically reduces the sluggishness that is otherwise typically present at low temperatures. Quantitative analysis of intensity-response functions also demonstrated that light sensitivity under substance P is significantly augmented. The plain temporal antagonism between these two modulators demonstrates that the visual system of Limulus possesses a well-poised mechanism which could be used to adjust the timing of its neural processing to interface well with the temporal characteristics of those visual stimuli that are currently present.

Mitigation of radiation-induced optic neuropathy in rats by ACE inhibitor ramipril: importance of ramipril dose and treatment time.

PURPOSE: Radiation-induced optic nerve damage was reduced by ramipril, a prodrug angiotensin-converting enzyme inhibitor (ACEI). This study was to determine the optimum dose and administration time of ramipril for mitigating radiation-induced optic neuropathy. MATERIALS AND METHOD: Adult Fischer 344 male rats were treated with a single dose radiation 30 Gy by using radiosurgical technique. After irradiation, the animals were randomly assigned into groups of different ramipril doses and administration time; control (no treatment), radiation alone, radiation+ramipril in different doses and starting times of drug. Ramipril was given 0.5-1.5 mg/kg/day and AT1R blocker Losartan 20 mg/kg/day in drinking water for 180 days. Functional endpoint with visual evoked potential (VEP) and anatomical endpoint with gross and histological analysis with immunohistochemical (IHC) stain were used. RESULTS: Normal VEP measurements in un-irradiated rats were 46.2+/-7.9 ms. There was no change of VEP value until 4 months, but was lengthened to 188.1+/-58.7 ms at 6 months after radiation. By ramipril treatment with the dose of 1.5 mg starting at 2 weeks after radiation, VEP was significantly shortened to 105.7+/-88.5 ms at 6 months. Gross and microscopic structure of the irradiated optic nerve was well preserved in the ramipril-treated group. CONCLUSION: Ramipril can mitigate the radiation-induced optic nerve damage and preserve the functional integrity of the nerve. The results support early treatment with a high dose of ramipril after radiation.

Light and alcohol evoked electro-oculograms in cystic fibrosis.

Cystic fibrosis (CF) is caused by a defect in the cystic fibrosis transmembrane conductance regulator (CFTR) which is a chloride channel. CFTR is expressed in the retinal pigment epithelium (RPE) where it is believed to be important in generating the fast oscillations (FOs) and potentially contributing to the light-electro-oculogram (EOG). The role of CFTR in the alcohol-EOG is unknown. We recruited six individuals with CF (three homozygotes for Delta508 and three heterozygous for Delta508) and recorded the light- and alcohol-EOGs as well as the FOs and compared them to a control group. The results showed that in the CF group the amplitude of the alcohol- and light-EOGs were normal. However, the time to peak of the light- and alcohol-rises were significantly faster than in the control group. We conclude that CFTR is not primarily responsible for the alcohol- or light-rises but is involved in altering the timing of these responses. The FOs showed differences between the homozygotes, heterozygotes and the controls. The amplitudes were significantly higher and the time to the dark troughs were significantly slower in the heterozygote group compared to both controls and the homozygotes. In contrast, the homozygotes did not differ in either amplitude or the timing of the FOs compared to the controls.

Ectopic expression of a microbial-type rhodopsin restores visual responses in mice with photoreceptor degeneration.

The death of photoreceptor cells caused by retinal degenerative diseases often results in a complete loss of retinal responses to light. We explore the feasibility of converting inner retinal neurons to photosensitive cells as a possible strategy for imparting light sensitivity to retinas lacking rods and cones. Using delivery by an adeno-associated viral vector, here, we show that long-term expression of a microbial-type rhodopsin, channelrhodopsin-2 (ChR2), can be achieved in rodent inner retinal neurons in vivo. Furthermore, we demonstrate that expression of ChR2 in surviving inner retinal neurons of a mouse with photoreceptor degeneration can restore the ability of the retina to encode light signals and transmit the light signals to the visual cortex. Thus, expression of microbial-type channelrhodopsins, such as ChR2, in surviving inner retinal neurons is a potential strategy for the restoration of vision after rod and cone degeneration.

Visual evoked potentials in neonatal hyperbilirubinemia.

The management of neonatal hyperbilirubinemia is very standardized. However, there is a lack of an objective method to evaluate the cerebral effects of bilirubin apart from brainstem auditory evoked potentials. There were few studies evaluating the effects of hyperbilirubinemia or phototherapy on the visual pathway in infants with hyperbilirubinemia. Serial visual evoked potentials of two groups of term neonates (N = 24)--group 1 with moderate hyperbilirubinemia (n = 16) and group 2 with severe hyperbilirubinemia (n = 8)--were evaluated prospectively. All infants had regular physical, neurologic, visual, and auditory evaluations until 3 years. Four (16%) had abnormal visual evoked potentials before 1 year, and the abnormalities returned to normal thereafter. There was no significant difference in visual evoked potentials between the two groups. All had normal neurodevelopmental status by 3 years, with the exception of one child from the severe group with ABO incompatibility with transient mild motor delay, hypotonia, and abnormal visual evoked potential. There were no abnormal effects of phototherapy on visual evoked potentials in infants with neonatal hyperbilirubinemia after 1 year of age. Although our sample size was small, the results suggest that the effects of hyperbilirubinemia on visual evoked potentials might be transient. (J Child Neurol 2006;21:58-62).

Deep brain stimulation of the subthalamic nucleus affects resting EEG and visual evoked potentials in Parkinson's disease.

OBJECTIVE: We studied changes of the EEG spectral power induced by deep brain stimulation (DBS) of the subthalamic nucleus (STN) in patients with Parkinson's disease (PD). Also analyzed were changes of visual evoked potentials (VEP) with DBS on and off. METHODS: Eleven patients with advanced PD treated with bilateral DBS STN were examined after an overnight withdrawal of L-DOPA and 2 h after switching off the neurostimulators. All underwent clinical examination followed by resting EEG and VEP recordings, a procedure repeated after DBS STN was switched on. RESULTS: With DBS switched on, the dominant EEG frequency increased from 9.44+/-1.3 to 9.71+/-1.3 Hz (P<0.01) while its relative spectral power dropped by 11% on average (P<0.05). Switching on the neurostimulators caused a decrease in the N70/P100 amplitude of the VEP (P<0.01), which inversely correlated with the intensity of DBS (black-and-white pattern: P<0.01; color pattern: P<0.05). CONCLUSIONS: Despite artifacts generated by neurostimulators, the VEP and resting EEG were suitable for the detection of effects related to DBS STN. The acceleration of dominant frequency in the alpha band may be evidence of DBS STN influence on speeding up of intracortical oscillations. The spectral power decrease, seen mainly in the fronto-central region, might reflect a desynchronization in the premotor and motor circuits, though no movement was executed. Similarly, desynchronization of the cortical activity recorded posteriorly may by responsible for the VEP amplitude decrease implying DBS STN-related influence even on the visual system. SIGNIFICANCE: Changes in idling EEG activity observed diffusely over scalp together with involvement of the VEP suggest that the effects of DBS STN reach far beyond the motor system influencing the basic mechanisms of rhythmic cortical oscillations.

Thalamic burst mode and inattention in the awake LGNd.

Awake mammals are often inattentive in familiar environments, but must still respond appropriately to relevant visual stimulation. Such "inattentive vision" has received little study, perhaps due to difficulties in controlling eye position in this state. In rabbits, eye position is exceedingly stable in both alert and inattentive states. Here, we exploit this stability to examine temporal filtering of visual information in LGNd neurons as rabbits alternate between EEG-defined states. Within a single second of shifting from alert to an inattentive state, both peak temporal frequency and bandwidth were sharply reduced, and burst frequency increased dramatically. However, spatial dimensions of receptive field centers showed no significant state dependence. We conclude that extremely rapid and significant changes in temporal filtering and bursting occur in the LGNd as awake subjects shift between alert and inattentive states.

[Changes of visual field and visual evoked potential in nasopharyngeal carcinoma patients after radiotherapy].

BACKGROUND & OBJECTIVE: Radiotherapy is the main treatment for nasopharyngeal carcinoma (NPC). The incidence of radiation-induced complications, especially radiation optic neuropathy (RON), increases along with prolonging survival time of the patients. This study was to investigate RON in NPC patients after irradiation by visual field and visual evoked potential (VEP) tests. METHODS: A total of 28 NPC patients, who underwent conventional external-beam irradiation, received visual field and VEP tests before irradiation, at the end of irradiation, and 5 years after irradiation. RESULTS: Thirty-four (60.7%) eyes in 21 patients developed pathological visual field; 15 (44.1%) of these 34 eyes occurred within 10-24 months after irradiation. Of the 34 eyes, 8 showed concentric visual field constriction; 6 showed bitemporal hemianopia; 8 showed local photosensitivity descend; 10 showed central or cecocentral scotoma; 2 showed scotoma enlargement. Forty-four (78.6%) eyes in 26 patients appeared VEP abnormity; 24 (54.5%) of these 44 eyes occurred within 14 months after irradiation. In small, medium, and large elements, VEP latencies were significantly longer within 1 year after irradiation than pre-irradiation (P < 0.001, P < 0.001, and P=0.001); VEP amplitudes were lower within 1 year after irradiation than pre-irradiation without significant difference (P=0.249, P=0.940, and P=0.450). One year after treatment, VEP latency delay maintained in each element (P=0.004, P < 0.001, P < 0.001); VEP amplitudes were decreased (P=0.002, P=0.189, P < 0.001). The incidence of pathologic visual field was significantly lower in patients received irradiation of < or =70 Gy than in patients received irradiation of > 70 Gy (50.0% vs. 77.3%, P=0.041). CONCLUSIONS: RON correlates to total irradiation dose. Pathologic visual field may indicate the position of RON.

Cognitive changes in short-term hypothyroidism assessed with event-related brain potentials.

Hypothyroidism is a common clinical problem during (131)Iodine-therapy of thyroid cancer. In the present investigation, possible cognitive dysfunction during hypothyroid state was assessed by means of neuropsychological tests and the recording of event-related brain potentials (ERPs). Fifteen patients undergoing therapy for thyroid cancer were examined twice: (1) substituted with thyroid hormones, (2) during hypothyroid state immediately prior to treatment. Standard neuropsychological tests were applied during both sessions and subjects showed a mild-to-moderate impairment in their hypothyroid state. In addition, ERPs were recorded from 19 scalp sites while subjects performed two visual search tasks. The serial task required the effortful one-by-one scanning of several items within a visual array, while the parallel task allowed processing of all stimulus items in parallel and automatically. ERPs showed a marked amplitude decrement and delay of the P3 component known to index the speed of stimulus evaluation and the amount of available processing resources. This effect was present only for the serial search task, while no changes were seen in the parallel search task. These data show that hypothyroidism during (131)Iodine-therapy is associated with clinically relevant cognitive dysfunctions, especially with effortful attention demanding tasks.

Evaluation of the effects of radiotherapy to the chiasm and optic nerve by visual psychophysical and electrophysiologic tests in nasopharyngeal carcinoma.

PURPOSE: To evaluate the effects of high-dose radiotherapy (RT) to the chiasm and optic nerves in locally advanced nasopharyngeal carcinoma patients by visual psychophysical and electrophysiologic tests. METHODS AND MATERIALS: A series of visual tests, including visual evoked potentials (VEPs), contrast sensitivity, and visual field and visual acuity tests, were administered to 27 patients with locally advanced (T4) nasopharyngeal carcinoma who had undergone RT to high doses 6 to 74 months previously. As a control group, the same tests were administered to 40 unirradiated patients who had been referred to the ophthalmology department for any reason. RESULTS: The median values of VEP latency, VEP amplitude, and contrast sensitivity and the rate of visual field defect were significantly worse in the RT group (p = 0.06, p <0.001, p <0.001, and p = 0.005, respectively). No dose-response relationship was found in any tests when 50 Gy was the cutoff value. However, a positive correlation between the interval after RT and VEP latency (r = 0.406, p = 0.003) and a negative correlation between the interval and contrast sensitivity (r = -0.499, p <0.001) was noted; no correlation could be established regarding VEP amplitude and the interval after RT. CONCLUSION: Radiation-induced injury to the anterior visual pathways could result in an increase in VEP latency and a decrease in VEP amplitude and contrast sensitivity. This injury seems to be a continuous process developing with time.

Modification of radiation injury by ramipril, inhibitor of angiotensin-converting enzyme, on optic neuropathy in the rat.

Inhibitors of angiotensin-converting enzyme (ACE) have been used to reduce radiation-induced normal tissue injury. The present study was carried out to determine whether ramipril, one of the inhibitors of ACE, would ameliorate radiation-induced brain damage, using a well-characterized optic neuropathy model in the rat, one of the most critical and radiosensitive structures in the brain. The brains of adult Fischer rats were irradiated stereotactically with 30 Gy using a single collimated beam. Six months after irradiation and 1.5 mg/kg day(-1) ramipril (started 2 weeks after irradiation), rats were assessed for optic nerve damage functionally, using visual evoked potential, and histologically. Results show that ramipril conferred significant modification of radiation injury, since rats receiving radiation alone showed a threefold lengthening in the mean peak latency in the visual evoked potential, whereas 75% of rats receiving radiation followed by ramipril had evoked potentials that resembled those of normal untreated control rats. The histology of irradiated and ramipril-treated optic nerves appeared nearly normal, while there was significant demyelination in both optic nerves of irradiated rats. The study represents the first demonstration of prophylaxis of radiation injury by a carboxyl-containing ACE inhibitor, providing a pharmacological strategy designed to reduce radiation-induced normal tissue damage.

Impairment of optic path due to radiotherapy for nasopharyngeal carcinoma.

PURPOSE: To evaluate the impairment of optic path caused by radiotherapy for nasopharyngeal carcinoma (NPC). METHODS: Visual evoked potential was used to evaluate the functional impairment of optic path by an 8 MV linear accelerator or 60Co gamma-ray radiotherapy in 63 (23 women and 40 men) patients with nasopharyngeal carcinoma before radiotherapy, at the end of radiotherapy, 6 months and 1, 2 and 3 years after their radiotherapy respectively. RESULTS: In the female group, the latency of VEP elicited by the three types of elements significantly delayed 2 and 3 years after radiotherapy than that before radiotherapy, at the end of radiotherapy, 6 months and 1 year after radiotherapy; there were no significant difference among VEP amplitudes elicited by the three types of elements before and after radiotherapy. In the male group, the latency of VEP elicited by the medium and the small elements significantly delayed 1 year after radiotherapy than that before radiotherapy and at the end of radiotherapy, the VEP latency elicited by the small elements was significantly prolonged 3 years after radiotherapy compared to that just after radiotherapy, while the VEP amplitude elicited by the large elements was significantly attenuated 1 year after radiotherapy compared to those before and just after radiotherapy. CONCLUSIONS: In the female group, the significant prolongation of VEP latency happened at the end of radiotherapy and lasted for 3 years, while the VEP amplitude did not change significantly during the 3 years after radiotherapy. It indicates that the sustained impairment by radiation within the female visual nerve system starts at the end of radiotherapy, but the impairment was mild. In the male group, the significant prolongation of VEP latency mostly happened 1 or 2 years after radiotherapy. It was shown that the radiotherapy for nasopharyngeal carcinoma certainly injured the optic path, and there was difference in the impairment between the two sexes.

[Change in visual evoked potential by radiotherapy of nasopharyngeal carcinoma].

OBJECTIVE: To study the effect of radiotherapy of nasopharyngeal carcinoma on visual evoked potential (VEP). METHODS: VEP of 63 patients with nasopharyngeal carcinoma were tested before, at the end of, half a year, one year, 2 years and 3 years after their radiotherapy. RESULTS: Within the male group, one year after radiotherapy, the latency of VEP was significantly delayed than that before and at the end of radiotherapy, while the amplitude was decreased significantly. Two years after radiotherapy, the latency of VEP was significantly delayed more than that before radiotherapy. However there was no significant difference among VEP at the end of, half a year and 3 years after radiotherapy. Within the female group, 2 years after radiotherapy, the latency of VEP was significantly delayed than that before radiotherapy. Three years after radiotherapy, the latency of VEP was significantly delayed than that before, at the end of, half a year and one year after radiotherapy. There was no significant difference in VEP amplitudes before and after radiotherapy. CONCLUSION: Within the male group, the abnormal delay of VEP latency mostly happens one or two years after radiotherapy. Within the female group, the significant delay of VEP latency happens at the end of radiotherapy and lasts for 3 years, while the VEP amplitude does not change significantly during the 3 years after radiotherapy. The result indicates that the sustained radiation damage within the female visual nerve system starts at the end of radiotherapy, but to a lesser degree. It was shown that radiotherapy of nasopharyngeal carcinoma certainly damages the visual nerve system, though there is sex difference in the impairment.

Single vs. paired visual stimulation: superposition of early neuromagnetic responses and retinotopy in extrastriate cortex in humans.

Neuromagnetic techniques were used in conjunction with magnetic resonance imaging (MRI) techniques to: (1) localize and characterize cortical sources evoked by visual stimuli presented at different locations in the lower right visual field; (2) examine the superposition of cortical responses by comparing the summation of responses to the presentation of single stimuli with responses to paired stimuli; and (3) examine the spatial resolution of magnetoencephalographic (MEG) techniques by comparing the identified source locations evoked by the presentation of single vs. paired stimuli. Using multi-dipole, non-linear minimization analyses, three sources were localized for each stimulus condition during the initial 80-170 ms poststimulus interval for all subjects. In addition to an occipital source, two extrastriate sources were identified: occipital-parietal and occipital-temporal. Each source evidenced a systematic shift in location associated with changes in stimulus placement parallel to the vertical meridian. To our knowledge, this is the first demonstration of retinotopic organization of extrastriate areas, using non-invasive neuromagnetic techniques. The paired presentation of stimuli reflected superposition of the responses evoked by single stimuli but only for early activity up to 150 ms poststimulus. Undersummation was evident after 150 ms. All sources identified for single stimuli were also identified in the paired-stimulus responses; but at the expense of larger errors for some of the estimated parameters.