Changes in pattern reversal evoked potentials during menstrual cycle

Cortical excitability in human somatosensory and visual cortex: implications for plasticity and learning - a minireview

The balance of excitation and inhibition plays a key role in plasticity and learning. A frequently used, reliable approach to assess intracortical inhibition relies on measuring paired-pulse behavior. Moreover, recent developments of magnetic resonance spectroscopy allows measuring GABA and glutamate concentrations. We give an overview about approaches employed to obtain information about excitatory states in human participants and discuss their putative relation. We summarize paired-pulse techniques and basic findings characterizing paired-pulse suppression in somatosensory (SI) and (VI) visual areas. Paired-pulse suppression describes the effect of paired sensory stimulation at short interstimulus intervals where the cortical response to the second stimulus is significantly suppressed. Simultaneous assessments of paired-pulse suppression in SI and VI indicated that cortical excitability is not a global phenomenon, but instead reflects the properties of local sensory processing. We review studies using non-invasive brain stimulation and perceptual learning experiments that assessed both perceptual changes and accompanying changes of cortical excitability in parallel. Independent of the nature of the excitation/inhibition marker used these data imply a close relationship between altered excitability and altered performance. These results suggest a framework where increased or decreased excitability is linked with improved or impaired perceptual performance. Recent findings have expanded the potential role of cortical excitability by demonstrating that inhibition markers such as GABA concentrations, paired-pulse suppression or alpha power predict to a substantial degree subsequent perceptual learning outcome. This opens the door for a targeted intervention where subsequent plasticity and learning processes are enhanced by altering prior baseline states of excitability.

Etiology of Idiopathic Macular Holes in the Light of Estrogen Hormone

The aim of this review was to identify a new potential explanation for the development of macular holes in relation to the female sex and to explain the possible underlying pathways. This approach was based on the evaluation of anatomical, physiological, and morphological analyses currently available in the literature. The findings showed that estrogen exerts a protective effect on the neuroretina and may influence Müller and cone cells. Both cell types are responsible for the building of the fovea structure. However, this protection may be lost due to the sudden decrease in estrogen levels during menopause. In conclusion, the fovea cones, through its sensitivity to estrogen and high energy consumption, may be very vulnerable to damage caused by a sudden changes in the concentration of estrogen in menopausal females. Such changes may result in cone degeneration, and thus a destroyed structure of the fovea, and may lead to the development of a hole in the fovea, as in the case of macular holes. This review revealed that under the decreasing influence of estrogen may cones play a key role with regard to the etiology of the development of macular holes. This aspect may be of strategic importance in prophylactic therapy for the prevention of the development of macular holes in premenopausal females or after ocular trauma.

Altered visual cortex excitability in premenstrual dysphoric disorder: Evidence from magnetoencephalographic gamma oscillations and perceptual suppression

Premenstrual dysphoric disorder (PMDD) is a psychiatric condition characterized by extreme mood shifts during the luteal phase of the menstrual cycle (MC) due to abnormal sensitivity to neurosteroids and unbalanced neural excitation/inhibition (E/I) ratio. We hypothesized that in women with PMDD in the luteal phase, these factors would alter the frequency of magnetoencephalographic visual gamma oscillations, affect modulation of their power by excitatory drive, and decrease perceptual spatial suppression. Women with PMDD and control women were examined twice-during the follicular and luteal phases of their MC. We recorded visual gamma response (GR) while modulating the excitatory drive by increasing the drift rate of the high-contrast grating (static, 'slow', 'medium', and 'fast'). Contrary to our expectations, GR frequency was not affected in women with PMDD in either phase of the MC. GR power suppression, which is normally associated with a switch from the 'optimal' for GR slow drift rate to the medium drift rate, was reduced in women with PMDD and was the only GR parameter that distinguished them from control participants specifically in the luteal phase and predicted severity of their premenstrual symptoms. Over and above the atypical luteal GR suppression, in both phases of the MC women with PMDD had abnormally strong GR facilitation caused by a switch from the 'suboptimal' static to the 'optimal' slow drift rate. Perceptual spatial suppression did not differ between the groups but decreased from the follicular to the luteal phase only in PMDD women. The atypical modulation of GR power suggests that neuronal excitability in the visual cortex is constitutively elevated in PMDD and that this E/I imbalance is further exacerbated during the luteal phase. However, the unaltered GR frequency does not support the hypothesis of inhibitory neuron dysfunction in PMDD.

Mapping changes in women's visual functions during the menstrual cycle: narrative review

BACKGROUND

This article systematically updates the literature on changes in visual functions during the phases of the normal menstrual cycle in women.

OBJECTIVES

To update Guttridge's 1994 review of visual structures and functions associated with the menstrual cycle and broaden the search through psychophysical, neuroimaging and neurobehavioral measurements covering 1994-2020.

DESIGN AND SETTING

Narrative review conducted in a neurosciences and behavior laboratory in Brazil.

METHODS

The PubMed, Cochrane Clinical Answers and Google Scholar databases were searched. After screening and applying the eligibility criteria, 32 articles were examined. Through this analysis, the following information was extracted: (1) geographical distribution of the study; (2) sample size (according to age and phase of the menstrual cycle); (3) type of measurements according to psychophysical, neuroimaging and neurobehavioral instruments; (4) vision testing model; (5) visual subcategory evaluated; (6) categories of processed visual stimuli; and (7) main findings.

RESULTS

The menstrual phases give rise to significant changes in visual functions, including in relation to orientation and spatial attention, visual campimetry and visual sensitivity. These relate specifically to the follicular and luteal phases.

CONCLUSIONS

These findings theoretically expand the effects of menstrual cycles on visual functions found by Guttridge (1994). Despite some inconsistencies in the studies analyzed, it was found that visual processing during the follicular and luteal phases of the normal menstrual cycle of healthy women can explain physiological, cognitive, behavioral and social modulations.

Menstrual Cycle Variations in Gray Matter Volume, White Matter Volume and Functional Connectivity: Critical Impact on Parietal Lobe

The role of gonadal hormones in neural plasticity remains unclear. This study aimed to examine the effects of naturally fluctuating hormone levels over the menstrual cycle in healthy females. Gray matter, functional connectivity (FC) and white matter changes over the cycle were assessed by using functional magnetic resonance imaging (fMRI), resting state fMRI, and structural MRIs, respectively, and associated with serum gonadal hormone levels. Moreover, electrocutaneous sensitivity was evaluated in 14 women in four phases of their menstrual cycle (menstrual, follicular, ovulatory, and luteal). Electrocutaneous sensitivity was greater during follicular compared to menstrual phase. Additionally, pain unpleasantness was lower in follicular phase than other phases while pain intensity ratings did not change over the cycle. Significant variations in cycle phase effects on gray matter volume were found in the left inferior parietal lobule (IPL) using voxel-based morphometry. Subsequent Freesurfer analysis revealed greater thickness of left IPL during the menstrual phase when compared to other phases. Also, white matter volume fluctuated across phases in left IPL. Blood estradiol was positively correlated with white matter volume both in left parietal cortex and whole cortex. Seed-driven FC between left IPL and right secondary visual cortex was enhanced during ovulatory phase. A seed placed in right IPL revealed enhanced FC between left and right IPL during the ovulatory phase. Additionally, we found that somatosensory cortical gray matter was thinner during follicular compared to menstrual phase. We discuss these results in the context of likely evolutionary pressures selecting for enhanced perceptual sensitivity across modalities specifically during ovulation.

Parallel modulation of intracortical excitability of somatosensory and visual cortex by the gonadal hormones estradiol and progesterone

The levels of the gonadal hormones estradiol and progesterone vary throughout the menstrual cycle thereby affecting cognition, emotion, mood, and social behaviour. However, how these hormones modulate the balance of neural excitation and inhibition, which crucially regulate processing and plasticity, is not fully understood. We here used paired-pulse stimulation to investigate in healthy humans the action of low and high estradiol and progesterone on intracortical inhibition in somatosensory (SI) and visual cortex (V1). We found that paired-pulse suppression in both SI and VI depended on estradiol. During high estradiol levels, paired-pulse suppression was significantly reduced. No comparable effects were found for progesterone, presumably due to a confounding effect of estradiol. Also, no hormone level-depending effects were observed for single-pulse evoked SEPs (somatosensory evoked potentials) and VEPs (visual evoked potentials) indicating a specific hormonal action on intracortical processing. The results demonstrate that estradiol globally modulates the balance of excitation and inhibition of SI and VI cortex.

Influence of Menstrual Cycle Phases on Neural Excitability in the Primary Somatosensory Cortex and Ankle Joint Position Sense

Introduction: Ankle sprain (AS) is one of the most common injuries among women engaged in competitive sports and recreational activities. Many studies have shown that several factors contributing to AS are influenced by the menstrual cycle. Despite the finding that abnormal joint position sense (JPS) is one of the major risk factors of AS, the alteration of the JPS throughout the menstrual cycle and its associated neural mechanisms remain unclear.

Objective: This study aimed to examine whether the menstrual cycle phases affect neural excitability in the primary somatosensory cortex (S1) and JPS.

Methods: Fourteen right-footed women participated in this study. Somatosensory-evoked potential and paired-pulse inhibition (PPI) were measured to assess S1 excitatory and inhibitory functions. Ankle JPS was measured using an active joint position matching method. Menstrual syndrome was evaluated using the menstrual distress questionnaire. All assessments were conducted in the follicular, ovulatory, and luteal phases.

Results: The two main findings of this study were as follows: First, PPI decreased in the ovulatory phase than in the follicular phase. This may have been the reason for estrogen altering the neural inhibition and facilitation balance throughout the menstrual cycle. Second, JPS was not changed during the menstrual cycle.

Conclusion: In conclusion, phases of the menstrual cycle affect the neural excitability in S1 as shown by the decreased PPI in the ovulatory phase, and the ankle JPS was unchanged throughout the menstrual cycle.

Illusory palinopsias induced by in vitro fertilization treatment: a case report

Background

In the current era, in vitro fertilization, a type of assisted reproductive technology, has been commonly used for infertility management and gestational surrogacy. The techniques that are routinely used in in vitro fertilization include ovarian hyperstimulation to generate multiple eggs, preparation of the ova and sperm, and culture and selection of resultant embryos before transfer into a uterus. These steps increase the chances of successful pregnancy following in vitro fertilization treatment many-fold, especially in young women. Complications reported with in vitro fertilization treatment include multiple gestations, ovarian hyperstimulation syndrome, and birth defects while ocular side effects reported include retinal detachment and progression of keratoconus. We report a case of visual illusory palinopsia following in vitro fertilization treatment in a patient with unexplained infertility.

Case presentation

A 31-year-old Asian woman was administered in vitro fertilization treatment for her unexplained infertility. She complained of visually disturbing flashes in her peripheral vision during her pregnancy. She described these flashes as occurring usually in the morning hours or while walking, coming in sets of three to four, occurring five–six times a day and lasting for less than 5–10 minutes. Her flashes were not accompanied by other ocular symptoms such as pain, redness, photophobia, or decrease in vision. Her ocular examination was normal. Neuroimaging with magnetic resonance imaging revealed no pathology. A diagnosis of visual illusory palinopsia secondary to in vitro fertilization treatment was made.

Conclusion

Disturbing visual palinopsia and afterimages can occur following in vitro fertilization treatment for infertility due to increased estrogen levels. This rare ocular side effect caused by in vitro fertilization treatment is not reported in the literature to the best of our knowledge. Gynecologists and/or infertility experts should educate their patients regarding these possible ocular symptoms. Even ophthalmologists should be aware of this rare cause for visual palinopsia.

Clomiphene citrate-induced visual hallucinations: a case report

BACKGROUND

Polycystic ovary syndrome is a common cause of chronic anovulation and infertility in otherwise healthy fertile couples. Clomiphene citrate is used as a first-line ovulation induction therapy in patients with polycystic ovary syndrome. Clomiphene citrate can cause both systemic and ocular side effects. We report a rare side effect of illusory palinopsias in a patient with polycystic ovary syndrome treated with ovulation induction therapy with clomiphene citrate, and emphasize the need for gynecologists and their patients to be aware of this rare ocular side effect.

CASE PRESENTATION

A 30-year-old Asian woman complained of persistent visual afterimages following treatment with 100 mg clomiphene citrate for anovulation. Her symptoms started on the fourth day after commencing the treatment and would last for 5 to 10 minutes. Similar visual symptoms were noted during her second cycle of treatment with clomiphene citrate. The severity of her symptoms reduced following the stoppage of the medication; however, the symptoms have persisted for more than 1 year since she stopped taking the drug.

CONCLUSIONS

Clomiphene citrate can cause disturbing illusory palinopsias. These afterimages persist even after stopping the infertility medication. It is a side effect not frequently seen by gynecologists or ophthalmologists. Gynecologists should make their patients aware of this rare ocular side effect when their patients start treatment with clomiphene citrate for infertility.

Shifts in Color Discrimination during Early Pregnancy

The present study explores two hypotheses: a) women during early pregnancy should experience increased color discrimination ability, and b) women during early pregnancy should experience shifts in subjective preference away from images of foods that appear either unripe or spoiled. Both of these hypotheses derive from an adaptive view of pregnancy sickness that proposes the function of pregnancy sickness is to decrease the likelihood of ingestion of foods with toxins or teratogens. Changes to color discrimination could be part of a network of perceptual and physiological defenses (e.g., changes to olfaction, nausea, vomiting) that support such a function. Participants included 13 pregnant women and 18 non-pregnant women. Pregnant women scored significantly higher than non-pregnant controls on the Farnsworth-Munsell (FM) 100 Hue Test, an objective test of color discrimination, although no difference was found between groups in preferences for food images at different stages of ripeness or spoilage. These results are the first indication that changes to color discrimination may occur during early pregnancy, and is consistent with the view that pregnancy sickness may function as an adaptive defense mechanism.

Estradiol levels during the menstrual cycle differentially affect latencies to right and left hemispheres during dichotic listening: an ERP study

Many behavioral studies have found high-estrogen phases of the menstrual cycle to be associated with enhanced left-hemisphere processing and low-estrogen phases to be associated with better right-hemisphere processing. This study examined the changing of hemispheric asymmetry during the menstrual cycle by analyzing event-related potential (ERP) data from midline and both hemispheres of 23 women during their performance of a dichotic tasks shown to elicit a left-hemisphere response (semantic categorization) and a right-hemisphere response (complex tones). Each woman was tested during her high-estrogen follicular phase and low-estrogen menstrual phase. Salivary assays of estradiol and progesterone were used to confirm cycle phase. Analyses of the ERP data revealed that latency for each hemisphere was differentially affected by phase and target side, such that latencies to the left hemisphere and from the right ear were shorter during the high-estrogen phase, and latencies to the right hemisphere and from the left ear were shorter during the low-estrogen phase. These findings supply electrophysiological correlates of the cyclically based interhemispheric differences evinced by behavioral studies.

Visual sensitivity to a conspicuous male cue varies by reproductive state inPhysalaemus pustulosusfemales

The vocal sac is a visually conspicuous attribute of most male frogs, but its role in visual communication has only been demonstrated recently in diurnally displaying frogs. Here we characterized the spectral properties of the inflated vocal sac of male túngara frogs (Physalaemus pustulosus), a nocturnal species, and túngara visual sensitivity to this cue across reproductive state and sex. We measured the spectral and total reflectance of different male body regions, including inflated and non-inflated vocal sacs, along with samples of the visual background against which males are perceived. Inflated vocal sacs were the most reflective of all body parts, being one log unit more reflective than background materials. We utilized an optomotor drum with black stripes and stripes that mimicked the spectral reflectance of the inflated vocal sacs with various nocturnal light intensities to measure the visual sensitivity thresholds of males,non-reproductive females and reproductive females. All three groups exhibited visual sensitivities corresponding to intensities below moonless conditions in open habitats or at the edge of secondary tropical forests. Reproductive females exhibited the greatest visual sensitivity of all groups, and were significantly more sensitive than non-reproductive females. Though the mechanism for this physiological difference between reproductive and non-reproductive females is unknown, it is consistent with previously observed patterns of light-dependent phonotaxic behavior in túngaras. We suggest that the visual ecology of the vocal sac, especially in nocturnal frogs,offers a rich source for investigations of visual ecology and physiological regulation of vision.

Long-term effects of tibolone on ocular functions in postmenopausal women

Hormone replacement therapy has been widely used for the prevention of postmenopausal osteoporosis and treatment of climacteric symptoms for many years, but its effect on ocular functions remains unclear. The aim of the study was to evaluate the long-term effects of tibolone on ocular functions in postmenopausal women. A total of 77 healthy women with at least 1 year of spontaneous menopause were enrolled in the study. Forty women were treated with tibolone for 6 months and 37 women were left untreated. All these patients underwent ophthalmic examination including visual acuity, intraocular pressure (IOP), tear functions, blue-on-yellow and white-on-white Humphrey visual field (HVF), visual evoked potentials (VEP) and electroretinography (ERG). There were significant differences in mean deviation of blue-on-yellow HVF, and oscillatory potentials (O1, O2, and O4) in the ERGs of the chronic tibolone users and the control (P < 0.0001, P = 0.001, P < 0.0001 and 0.05, respectively). However, no significant differences were observed in visual acuity, IOP, tear functions, white-on-white HVF and VEP. We concluded that, although tibolone had no effects on visual acuity, IOP, tear functions and VEP, it might cause some early adverse effects on the electrophysiologic and structural characteristics of the retina, which are detected by these sensitive assays. Randomized placebo-controlled studies with larger groups are needed in future research.

Color naming deficits and attention-deficit/hyperactivity disorder: a retinal dopaminergic hypothesis

BACKGROUND

Individuals with Attention-Deficit/Hyperactive Disorder (ADHD) have unexplained difficulties on tasks requiring speeded processing of colored stimuli. Color vision mechanisms, particularly short-wavelength (blue-yellow) pathways, are highly sensitive to various diseases, toxins and drugs that alter dopaminergic neurotransmission. Thus, slow color processing might reflect subtle impairments in the perceptual encoding stage of stimulus color, which arise from hypodopaminergic functioning.

PRESENTATION OF HYPOTHESES

1) Color perception of blue-yellow (but not red-green) stimuli is impaired in ADHD as a result of deficient retinal dopamine; 2) Impairments in the blue-yellow color mechanism in ADHD contribute to poor performance on speeded color naming tasks that include a substantial proportion of blue-yellow stimuli; and 3) Methylphenidate increases central dopamine and is also believed to increase retinal dopamine, thereby normalizing blue-yellow color perception, which in turn improves performance on the speeded color naming tasks.

TESTING THE HYPOTHESIS

Requires three approaches, including:1) direct assessment of color perception in individuals with ADHD to determine whether blue-yellow color perception is selectively impaired; 2) determination of relationship between performance on neuropsychological tasks requiring speeded color processing and color perception; and 3) randomized, controlled pharmacological intervention with stimulant medication to examine the effects of enhancing central dopamine on color perception and task performance

IMPLICATIONS OF HYPOTHESIS

If substantiated, the findings of color perception problems would necessitate a re-consideration of current neuropsychological models of attention-deficit/hyperactivity disorder, guide psycho-education, academic instruction, and require consideration of stimulus color in many of the widely used neuropsychological tests.

The effects of menstrual cycle on the knee joint position sense: preliminary study

The purpose of this study was to determine the effects of menstrual cycle on proprioception by using the active knee joint position sense test (JPST). The 19 healthy women (ages between 20 years and 27 years) who have normal regular menstrual cycle were included in the study. We applied JPSTs at two different directions throughout the three different phases of the menstrual cycle, i.e. menstrual, follicular, and early luteal in dominant knees. When we started from flexion (90 degrees ), target angles were 70 degrees , 50 degrees , and 30 degrees and we started from extension (0 degrees ), target angles were 20 degrees , 40 degrees and 60 degrees . The absolute reposition errors from the target angles have been evaluated. Results have shown that reposition errors from the target angle at 40 degrees , 50 degrees and 70 degrees of knee angles were higher in the menstrual phase than that of the follicular phase (P<0.05). In addition, higher value of reposition error from the target angle at 40 degrees was found in the menstrual phase compared to luteal phase (P<0.05). In conclusion, we have demonstrated that active JPST was significantly reduced in the menstruation period.

Spectral and Coherent Characteristics of EEG in Women during Various Phases of Menstrual Cycle

EEG recording was performed in healthy women during various phases of menstrual cycle. Comparative study showed that the power spectrum of EEG a-waves in central and medio-temporal areas significantly decreases during ovulation. In the menstrual phase coherent characteristics of EEG alpha-waves increased in symmetrical occipital and intrahemispheric parieto-occipital areas.

Menstrual Cycle-Dependent Changes in White-on-White Visual Field Analysis of Diabetic Women

AIM

To determine the effect of the menstrual cycle on white-on-white perimetry (WWP) tests of diabetic women.

SUBJECTS AND METHODS

Left eyes of 129 normally menstruating women (81 type 1 diabetes mellitus (DM) with mild (n = 43) and severe (n = 38) non-proliferative diabetic retinopathy (NPDR), and 48 healthy control females) were included in the study. All subjects underwent complete ocular examination and WWP tests both in the follicular (7-10th day of the cycle) and luteal phases (days 3-7 before the bleeding) of two consecutive menstrual cycles. WWP was performed using Humphrey Field Analyzer II with SITA Standard, central 30-2 program. Mean sensitivity (MS) of points located at central 3, 9, 15, 21 and 27 degrees retinal locations (4, 12, 18, 24 and 16 points, respectively) were calculated in all menstrual phases.

RESULTS

The mean age of diabetic patients with mild and severe NPDR and control subjects were 28.8 +/- 4.7, 30.1 +/- 5.9 and 29.4 +/- 5.1 years, respectively (p > 0.05). Their mean MS values were 30.7 +/- 1.0, 30.4 +/- 1.0 and 30.8 +/- 0.8 dB, respectively (p > 0.05). Diabetic patients with severe NPDR demonstrated significant decreases in mean MS values of peripheral 21 and 27 degrees visual field locations in the luteal phase (p < 0.05). However, changes in that of the locations within central 15 degrees visual field were non-significant (p > 0.05). Diabetic patients with mild NPDR and control subjects demonstrated no significant changes in mean MS values of any of the visual field locations (p > 0.05).

CONCLUSION

Peripheral, rather than central, locations of central visual field of diabetic women with severe NPDR demonstrated a significant retinal sensitivity loss in the luteal phase. These findings should be taken into consideration during the clinical follow-up of diabetic women at risk of glaucoma and ocular hypertension.

Visual sensitivity across the menstrual cycle

This study was designed to evaluate the hypothesis that hormonal change can affect lower level light-adaptation processes, which are likely to be retinally based. Foveal visual sensitivities were measured across several menstrual cycles of four women not using hormonally acting medication and across several menstrual cycles of three women using a triphasic oral contraceptive. One woman, diagnosed with premenstrual syndrome (PMS), was a subject for both groups. Sensitivities were measured for a series of test wavelengths for 580-nm backgrounds of 2.0 and 4.0 log td. Of the six individuals tested, one had clear evidence of visual-adaptation changes occurring in phase with the menstrual cycle. Prior to using the oral contraceptive, this individual (the PMS subject) experienced changes of short-wavelength-sensitive (SWS)-cone-mediated sensitivities of up to about 1.4 log unit on the 4.0 log td background. Her SWS-cone-mediated sensitivities tended to be highest near ovulation and lowest premenstrually. Threshold-versus-illuminance (TVI) curves confirmed that the rate of sensitivity decrease with increasing background illuminance (i.e. the TVI slope) was greater premenstrually. The degree of background-induced desensitization within her middle-wavelength-sensitive (MWS)/long-wavelength-sensitive (LWS) cone pathways also appeared to vary cyclically, but the magnitude of the variation was smaller and the time course appeared to be different. When this subject began oral contraceptive use, the patterns of sensitivity change were all altered. None of the other five subjects experienced changes of SWS-cone-mediated vision that were cyclic and significantly adaptation-state dependent. However, there was evidence for a limited degree of cyclic adaptation change within the MWS/LWS cone pathways of at least one additional subject. We conclude that hormonal change can--for some unknown proportion of women--be linked to alterations of retinal function. However, the alterations are not the same for all visual pathways, and there are pronounced individual differences. The data also demonstrate that individuals' visual adaptation capabilities can vary substantially over periods of weeks.

Can whole brain nerve conduction velocity be derived from surface-recorded visual evoked potentials?

Reed, Vernon, and Johnson [Reed, T. E., Vernon, P. A., & Johnson, A. M. (2004). Sex difference in brain nerve conduction velocity in normal humans. Neuropsychologia, 42, 1709-1714] reported that "nerve conduction velocity" (NCV) of visual transmission from retina to the primary visual area (V1) is significantly faster in males than females. The authors estimated the NCV by dividing head length (nasion-to-inion distance) by the latency of the well-known P100 component of the visual evoked potential (VEP). Here, we critically examine these metrics and we contend that knowledge of the underlying physiology of neural transmission across the initial stages of the visual processing hierarchy dictates that a number of their assumptions cannot be reasonably upheld. Alternative, and we believe, more parsimonious interpretations of the data are also proposed.

Assessment of the effectiveness of postmenopausal tibolone therapy on neural functions by measuring visual evoked potentials: a placebo-controlled study

OBJECTIVE

To assess the effect of hormone replacement therapy on neural transmission in postmenopausal women using tibolone by a non-invasive, objective way.

STUDY DESIGN

In a randomised, 3 cycle, placebo-controlled study, neurovisual transmission in optic pathways were evaluated by measuring visual evoked potentials (VEP). After neuroophtalmologic examination, eligible subjects were randomised into two groups. Treatment group (n=38) were given tibolone 2.5mg daily continuously for 3 months and control group (n=20) were treated with placebo. A baseline VEP measurement before the treatment and then at the end of first, second and third month were obtained by the EMG-evoked system in the Department of Neurology, University of Celal Bayar, Manisa, Turkey.

RESULTS

Data from 31 women from treatment group and 16 from control group were available for evaluation. The mean P(100) latency values, which indicate the transition time period between the optic stimuli and electrical change recorded on the occipital area by the skin electrodes, have showed a significant decrease for the study group (from 100.39+/-0.58 to 97.90+/-0.65 ms, P<0.01) at the end of the first month of treatment according to the baseline values. This difference between two groups has remained constant during the study period.

CONCLUSION

The change in latency measurements of VEP, reflecting the functional status in optic pathways from retina to occipital cortex were significantly different in the treatment group than in that of control. We concluded that a facilitating effect of tibolone was observed on neurovisual transmission.

Sex differences in response to red and blue light in human primary visual cortex: a bold fMRI study

Studies using a variety of investigative methods, including functional brain imaging and electroencephalography (EEG), have suggested that changes in central nervous system (CNS) dopamine function result in altered visual system processing. The discovery of abnormal retinal blue cone, but not red cone, electroretinogram in association with cocaine withdrawal and Parkinson's disease suggests that visual system response to blue light might be a marker for CNS dopamine tone. As there are numerous sex-related differences in central nervous system dopamine function, we predicted that blue and red light stimulation would produce sex-specific patterns of response in primary visual cortex when studied using the blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) technique. We analyzed the BOLD response to red and blue light in male and female human volunteers (N=20). Red and blue light responses in primary visual cortex (V1) to stepped intensities of red and blue light were compared by sex for threshold to detectable BOLD signal increase and for stimulus intensity vs. BOLD signal response. Near threshold, males and females showed similar BOLD signal change to red light, but males showed a threefold greater increase (0.52%) to blue light stimulation when compared to females (0.14%). Log-linear regression modeling revealed that the slope coefficients for the red light stimulus intensity vs. signal change curve were not significantly different for males and females (z=0.995, P=0.320), whereas the slope coefficients for the blue light stimulus intensity vs. signal change curve were significantly larger in males (z=2.251, P=0.024). These findings support a sex and color-dependent differential pattern of primary visual cortical response to photic stimulation and suggest a method for assessing the influence of specific dopamine agonist/antagonist medications on visual function.

Estrogen and visual hallucinations in a patient with Charles Bonnet syndrome

PURPOSE

To describe the occurrence of visual hallucinations in a patient with Charles Bonnet syndrome associated with estrogen intake.

METHOD

Case report.

RESULTS

An 84-year-old woman with poor visual acuity secondary to bilateral, nonexudative, age-related macular degeneration had nonthreatening visual hallucinations 2 weeks after starting oral estrogen for osteoporosis. The estrogen was stopped, and the hallucinations subsided. The patient was given estrogen twice more and each time the hallucinations recurred.

CONCLUSION

We report a case of Charles Bonnet syndrome associated with estrogen intake in an 84-year-old woman. Estrogen may have promoted release phenomena and triggered the hallucinatory episodes in our patient.

Effects of oestrogen replacement therapy on pattern reversal visual evoked potentials

As a result of a regression in the ovarian functions, oestrogen level in circulation during the menopause drops to 1/50 of its value in the normal reproductive cycle. Excitatory oestrogen increases the sensitivity of the central nervous system to catecholamines by changing the opening frequency of voltage-related L-type calcium channels and augmenting the effect of glutamate; in addition it inhibits the formation of gamma-amino butyric acid (GABA) by the inhibition of glutamate decarboxylase enzyme. It is argued that oestrogen increases transmission in the optic pathways and that oestrogen is responsible for the shorter latency values and higher amplitudes of visual evoked potentials in women. We recorded the monocular pattern reversal visual evoked potentials (PRVEP) of both eyes of 54 post-menopausal women before treatment and of 30 of them after replacement therapy with Tibolon, and of 24 women receiving placebo treatment. The explicit values of P100 latency of right and left eyes before treatment were 98.8 +/- 3.5 and 99.0 +/- 3.3 ms, respectively. The explicit values of P100 latency of right and left eyes after placebo treatment were 98.6 +/- 3.7 and 98.8 +/- 4.0, respectively. The explicit values of P100 latency of right and left eyes after replacement treatment were 94.6 +/- 3.7 and 94.8 +/- 4.0, respectively. We found a statistically significant decrease in the mean PRVEP latencies and a statistically significant increase in mean amplitudes after replacement treatment (P < 0.001) compared with those before treatment and those after placebo treatment. We attributed the changes in PRVEP values after replacement treatment to the action of Tibolon, which acted as a natural sex steroid and speeded the visual transmission time via the widespread receptors in the central nervous system. It is concluded that PRVEP is an objective electrophysiological assessment method in evaluating the efficiency of hormone replacement therapy in post-menopausal women.