J.Neurol.Sci.[Turk] Journal of Neurological Sciences [Turkish] 29:(4)# 33; 676-688, 2012 http://www.jns.dergisi.org/text.php3?id=587 Research Article Language Asymmetry and Hormonal Fluctuations During The Menstrual Cycle Handan CAN1, Constanze HAHN2, Sebastian OCKLENBURG2, Anna BALL2, Onur GÜNTÜRKÜN2 1Faculty of Arts and Sciences,Uludağ University, Department of Psychology, Görükle/Bursa, Türkiye 2Institute of Cognitive Neurosicence, Ruhr University, Faculty of Psychology, Bochum , Almanya Summary Objective: The aim of this study was to investigate hormone-asymmetry relationships during the menstrual cycle for both hemispheres using verbal dichotic listening task. Method: This study was conducted with thirty-two normally cycling women; all of them were native German speakers and right-handed with no use of hormonal medication in the previous 6 months. STCI-S18, a questionnaire to assess current mood, the Edinburgh Handedness Inventory, a background questionnaire to collect demographic information, the Symptom-Checklist 90-R and a verbal dichotic listening task were administered to all participants /completed by all participants. Result: Statistical analysis indicated that the main effect of ear was significant (p=.007). A right ear advantage was observed, but neither the main effect of cycle (p=.303) nor the interaction of ear and cycle (p=.955) was significant. We did find, however, a significant main effect of cycle on auditory recognition when we analyzed the data of the 17 participants with validated estradiol changes (p=.047). Conclusion: The results of the dichotic listening task data showed that the degree of language asymmetry as revealed by dichotic listening did not change during the three menstrual phases. We did find, however, that the main effect of cycle was significant when we analyzed the data of 17 participants with available estradiol levels. Estradiol seems to affect overall auditory recognition without altering asymmetry. Key words: Verbal dichotic listening, language asymmetry, hormonal fluctuations, menstrual cycle Dil Asimetrisi ve Menstrüel Siklusta Hormonal Değişiklikler Özet Amaç: Çalışmanın amacı sözel dikotik dinleme görevi kullanarak her iki hemisfer için menstrual siklüs sırasında hormon- asimetri ilişkilerini incelemektir. Yöntem: Bu çalışma son 6 ay içinde hormon içeren ilaç kullanmamış, sağ elini kullanan ve hepsi Alman vatandaşı olan 32 normal menstrual siklüs gösteren kadın katılımcı üzerinden yürütülmüştür. Tüm katılımcılara bir mod değerlendirme anketi olan STCI-S18, Edingburgh El Tercihi Envanteri, demografik bilgileri içeren özgeçmiş formu, Semptom Tarama 90-R and sözel dikotik dinleme görevi uygulanmıştır. Bulgular: İstatistiksel analiz kulak temel etkisinin anlamlı olduğunu göstermiştir (p=.007). Sağ kulak avantajı gözlenmiş; ancak ne siklüs temel etkisi (p=.303) ne de kulak ve siklüs etkileşimi (p=.955) anlamlı bulunmamıştır. Yine de 17 kişilik grubun verisi üzerinden yapılan analizde siklüs temel etkisi anlamlı bulunmuştur (p=.047). 676 J.Neurol.Sci.[Turk] Sonuç: Dikotik dinleme (sözel) görevi veri sonuçları, dikotik dinleme görevinde ortaya çıkan dil asimetrisi derecesinin, menstrüel siklüsün üç fazında da değişmediğini göstermiştir. Ancak yine de, uygun östradiol düzeylerine sahip 17 katılımcının veri analizinde, siklüs etkisi anlamlı bulunmuştur. Östradiol asimetriyi değiştirmeden işitsel tanımayı etkiler gibi gözükmektedir. Anahtar Kelimeler: Sözel dikotik dinleme, dil asimetrisi, hormonal dalgalanmalar, menstrual siklüs INTRODUCTION this effect is present for left- and right-hemispheric tasks, they assumed that P Cerebral asymmetries affect most aspects modulates the interhemispheric inhibition of the cognitive architecture of the human via the corpus callosum(19,18). This brain. To some extent asymmetries are sex- transcallosal interaction is thought to be an dependent, with differences between the essential mechanism in causing functional right and left hemispheres being more asymmetries(6,11). pronounced in men than in women. Although these differences are not evident The effects of sex hormones have been in all studies, meta-analyses clearly reveal explored in normally cycling women in their existence(40). Some of the sex effects several studies (7,4,8,19,18), but with partly on lateralization are possibly related to conflicting findings. Some of the gonadal steroid hormone levels in contradictions reported above could result women(13). Consequently, sex hormonal from a lack of measuring the actual fluctuations during the menstrual cycle hormonal levels of the participants. modulate left-right differences(19,18). Instead, researchers had simply estimated Several hypotheses have been proposed to the day of the menstrual cycle by counting explain the influence of sex hormones on backwards from the expected start date of functional cerebral asymmetries (FCAs). the next menstrual bleeding (22). Thus, only Heister et al.(21) suggested that increased studies that actually obtain hormonal levels of sex hormones in the menstrual assays should be cycle were associated with reduced FCAs conducted (2,43,17,10,19,18,31,35,12). in both the right and the left hemisphere. The second possible explanation for the On the other hand, McCourt et al.(30) discrepancies in the results of the previous provided evidence that high levels of sex studies may be related to the fact that the hormones cause an increase in FCAs in effects of hormones on FCAs may be task- tasks that are dominated by the left (LH) or dependent(15,16,21,31,35,37). Previous studies the right hemisphere (RH). The author of have used figure recognition(4), cognitive another previous study about the influence and motor tests(15,16) and spatial of hormones on human cognitive and bisection(30) and found greatest motor skills(16) proposed that high levels of asymmetries during the midluteal phase. estrogen led to opposite effects for each Other studies, however, included figural hemisphere, causing an increase of LH and comparisons(35) and decisions about a decrease of RH performance. In one faces(21) and discovered the most study that controlled for hormone prominent asymmetries during menses. concentration and for repeated measures, the authors(19) identified interactions In the present study, we examined between the cycle phase and FCAs for both functional cerebral asymmetries using the right- and left-hemispheric dominant tasks. dichotic listening task. Similar to our Hausmann and Güntürkün(19) proposed that study, the cycle-related change of FCAs high levels of progesterone (P) are related during the menstrual cycle has already to a reduction of lateralization. Because been investigated in previous studies using dichotic listening(41,37,12). We investigated 677 J.Neurol.Sci.[Turk] cycle-related change in FCAs with a information, family, hormonal, medical detailed analysis of relevant hormones to and educational history, and the Symptom- verify the three relevant cycle phases Checklist 90-R(14) were completed by all (menses, follicular and midluteal). To this participants at the beginning of the first end, we collected saliva from all of the session. The computerized dichotic participants to measure estradiol (E) and listening (DL) task was administered at progesterone (P) levels. We also aimed to each of the three sessions (during the investigate hormone/asymmetry menstrual (days 2-5), follicular (days 8-11) relationships during the menstrual cycle. and midluteal phases (days 20-22). For this aim, we performed verbal dichotic listening as a left-hemispheric dominant The verbal DL task usually reveals a right task. ear advantage that corresponds to left hemisphere superiority. In this task, MATERIAL AND METHODS pseudorandomly arranged syllable pairs Participants that were presented dichotically through closed system headphones at 80 dB were This study was conducted using thirty-two presented. The stimulation set also normally cycling women with a mean age included diotic (homonym) stimuli, which of 25.23 years (S.D.=4.57, age range: 19- consisted of two identical sounds. The 38) and a regular menstrual cycle of 25 to stimuli were digitally recorded, natural, 31 days. All participants were German complex speech sounds that were produced citizens and were right-handed. Right- by a male, German, adult voice. The handedness was controlled using the classical vowel (CV) syllables “BA”, Edinburgh Handedness Inventory (EHI; “DA”, “GA”, “KA”, “PA” and “TA” with 32). The asymmetry index (LQ) provided a mean duration of 350 ms were used. The by this test was calculated using [R- basic sound characteristics, such as the L)/(R+L)] x 100, leading to values between intensity of the auditory stimuli/CV -100 and +100. Dextrality was indicated by syllables, were controlled and balanced. positive values, whereas sinistrality was While forming the dichotic syllables, indicated by negative values in this index. spectral temporal envelopes of the The mean handedness score was 84.11 syllables were matched. All of the possible (S.D.=15.08; range: 47-100). None of the combinations of the syllables pairs were participants had used hormonal pills or presented to both ears, resulting in 36 medication in the previous 6 months. All possible combinations. To observe the participants had normal or corrected-to- possible differences between the right and normal visual acuity; none of them had a left hand responses, the participants were hearing threshold higher than 30 dB, and presented 72 (one round for the right hand the interaural difference was never higher and one round for the left hand 2 x 36 x 2 than 10 dB. The participants were recruited CV pairs) dichotic syllable pairs per hand, using an announcement and were paid for leading to a total of 144 stimuli. their participation. Participants were Participants were tested three times (during randomly assigned to the experimental their menses, follicular and midluteal groups, and written informed consent was phases) during their cycle. obtained from every participant. The State-Trait-Cheerfulness Inventory Materials (STCI-S18; 36) was used to assess the In this study, both paper-pencil tests and current mood of the participants during computerized tasks were used. A German different phases of their menstrual cycle. mood questionnaire, the Edinburgh STCI-S18 is an instrument that measures Handedness Inventory, a background the three concepts of cheerfulness, questionnaire to collect demographic seriousness and bad mood. Each concept 678 J.Neurol.Sci.[Turk] include six items, and the responses were mixture was used for the hormonal given on a 4 point rating scale (strongly analysis. Immediately after the collection disagree, 1; moderately disagree, 2; of sample, these saliva samples were stored moderately agree, 3; and strongly agree, 4). at -22°C until all of the participants Procedure completed all of the three sessions. Saliva E and P levels were determined using Participants started with their first testing Chemiluminescence assay (CLIA) by an session independent of their individual independent professional hormone cycle day, and the date of the first laboratory that used commercial hormone experiment was planned according to the assays. This study was approved by the information given by the participant. Every Ethics Committee of the Faculty of participant was tested three times: once Psychology at the Ruhr-University during the menstrual phase (between the Bochum, Germany. second and the fifth day of their cycle), once during the follicular phase and once RESULTS during the midluteal phase. To control for Salivary Assay potential repeated measures effects, the women were tested in a counterbalanced We first calculated the percent increase of order, starting with either the menstrual, the E and P levels during the follicular and follicular or midluteal phase of the the luteal phase compared to the menstrual menstrual cycle. All of the participants phase. We defined that subjects had to completed all of the three sessions during a display a 45% increase during the single menstrual cycle, with the exception follicular and the luteal phase for E and P, of three participants who could not come to respectively. All together, 20 participants their appointments because of personal had to be excluded. The mean level of reasons, and who completed the sessions in serum P in the remaining 12 women was the subsequent menstrual cycle. All of the 156.38 pg/ml during the menstrual phase three sessions were performed at the same and 571.39 pg/ml during the midluteal time of the day for each participant to phase. A paired t-test revealed a significant control for circadian variability in hormone difference in the mean saliva P levels releases. In addition, all of the participants between the menstrual and follicular were requested not to eat or drink phases (t (11) = 6.13, p<.001). The mean anything, except for water, for at least one level of serum E was 1.47 pg/ml during the hour before the experiment. menstrual phase and 6.94 pg/ml during the follicular phase. A paired t-test revealed a Prior to the first experimental session, the significant difference in the mean serum E background questionnaire created by levels between the menstrual and follicular Biopsychology Department of Ruhr phases (t (11)=5.14, p<.001). University, a mood questionnaire (STCI– S18), the Edinburgh Handedness Verbal Dichotic Listening Inventory, a hearing acuity measurement The data from the 12 normally cycling and the Symptom Checklist 90-R(14) were women that met the E and P level criteria performed for all participants with a were analyzed using parametric statistics consent form, and the STCI–S18 was because the Kolmogorov–Smirnov repeated during each of two other sessions. Goodness-of-Fit test showed normal After the completion of the paper-pencil distributions for all variables. First, the tests, a saliva sample was collected from data were calculated with a one-way all participants two times: once before and analysis of variance (ANOVA) with once after each session. To account for the repeated measures and then we performed hormonal changes during the session, the a 2 x 3 (ear and cycle) analysis of variance two saliva samples were mixed, and this (ANOVA) with repeated measures to the 679 J.Neurol.Sci.[Turk] data. The Greenhouse-Geisser procedure 1). A 2 x 3 (ear x cycle) analysis of with epsilon corrected degrees of freedom variance (ANOVA) with repeated was used if the data showed significant measures was also conducted on reaction deviations from sphericity. Neither the time (RT) mean value data. the result of main effect of cycle (F (2, 22)=1.25, this analysis indicated that neither the main p=.303) nor the interaction of ear and cycle effect of ear F (1, 11)=3.57, p=.09) nor (F (2, 22)=.04, p=.955 ns) was significant. cycle (F (2, 22)=.131, p=.817 ns) was However, a 2 x 3 (ear and cycle) analysis significant. The interaction of ear and cycle of variance (ANOVA) with repeated (F (2, 22)=2.31, p=.138 ns) was not measures indicated that the main effect of significant, either. Additionally, the results ear was significant (F (1, 11)=10.90, of the one way ANOVA with repeated p=.007). A right ear advantage (REA) was measures conducted over laterality index observed; the percentage of correct (LI), the percent correct scores, RT mean, answers obtained from the right ear was RT median and RT variance indicated that higher than that obtained from the left ear the main effect of cycle over these data during all the three cycles (Table 1; Figure was not significant. Figure 1: Main Effect of Ear over Correct Answers of 12 Subjects in DL (verbal) Task Three Phases Table1. Main Effect of Ear over Correct Answers of 12 Subjects in DL (verbal) Task Three Phases CYCLE MENSTRUAL FOLLICULAR LUTEAL EAR Mean SD Mean SD Mean SD RE 71.25 23.02 70.50 24.60 70.42 19.76 LE 33.25 21.77 31.67 20.42 32.00 17.27 680 J.Neurol.Sci.[Turk] We then identified the participants with was due to an REA with the percentage of confirmed P levels during the menstrual correct answers obtained from the right ear and midluteal phases and conducted the being higher than those from the left ear data analyses with 20 participants that met (Table 2; Figure 2). A 2x 2 (ear x cycle) the required criteria. A paired t-test analysis of variance (ANOVA) with revealed a significant cycle-phase repeated measures was also conducted on difference in mean serum P level (t RT mean value data (Table 3; Figure 3). (19)=7.54, p <.001). The data from the 20 The result of this analysis indicated that the normally cycling women were analyzed main effect of ear was significant (F using parametric statistics because the (1,19)=4.91, p=.040). This was due to the Kolmogorov–Smirnov Goodness-of-Fit RT mean value obtained from the right ear test showed normal distributions for all being faster than those from the left ear variables. The data were calculated using a (Table 3; Figure 3). However, again, 2 x 2 (ear x cycle) with repeated measures. neither the main effect of cycle (F Neither the main effect of cycle (F (1,19)=2.61, p=0.123 ns) nor the (1,19)=2.74, p=0.114 ns) nor the interaction of cycle and ear (F (1,19)=0.35, interaction of ear and cycle (F (1,19)=0.19, p=0.563 ns) was found to be significant. p=0.666 ns) was significant. However, a 2 And the results of one way ANOVA with x 2 (ear x cycle) analysis of variance repeated measures conducted over LI, the (ANOVA) with repeated measures again percent correct, RT mean, RT median and indicated that the main effect of ear was RT variance indicated that main effect of significant (F (1,19)=36.25, p<.001). This cycle over these data was not significant. Table 2. Main Effect of Ear over Correct Answers of 20 Subjects in DL (verbal) Task during Two Phases CYCLE EAR MENSTRUAL LUTEAL Mean SDr Mean SD RE 78.30 21.55 77.05 19.69 LE 28.15 19.32 27.85 16.03 Figure 2: Main Effect of Ear over Correct Answers of 20 Subjects in DL (verbal) Task during Two Phases 681 J.Neurol.Sci.[Turk] Table 3. Main Effect of Ear over RT Mean of 20 Subjects in DL (verbal) Task during Two Phases CYCLE MENSTRUAL LUTEAL EAR Mean SD Mean SD RE 1158.91 141.03 1188.34 138.04 LE 1186.37 158.64 1226.68 172.58 Figure 3: Main Effect of Ear over RT Mean of 20 Subjects in DL (verbal) Task during Two Phases We also examined whether an analysis again indicated because the percentage of conducted using those participants with correct answers obtained from the right ear available E levels would yield clearer was higher than that from the left ear results. For this aim, we identified 17 during all three cycles. The results of a 2 x participants whose E levels were 2 (ear x cycle) analysis of variance significantly higher during the follicular (ANOVA) with repeated measures phase than during the menstrual phase. We conducted for the RT mean values also confirmed these levels using a hormone indicated that the main effect of ear was assay and analyzed the data of these significant (F (1,16)=10.25, p=.006). This participants. A paired t-test revealed a was again due to the RT mean value significant cycle-phase difference in mean obtained from the right ear being faster serum E levels (t (16)=5.26, p<.001). We than those from the left ear (Table 6; analyzed the data using 2 x 2 (ear x cycle) Figure 6). However, neither cycle (F analysis of variance (ANOVA) with (1,16)=0.63, p=.438) nor the interaction of repeated measures. This analysis indicated ear and cycle was significant (F that the main effect of ear (F (1,16)=24.07, (1,16)=0.10, p=.997). The results of one p<.001) (Table 4; Figure 4) and cycle (F way ANOVA with repeated measures (1,16)=4.63, p=.047) (Table 5; Figure 5) conducted over LI, the percent correct, RT was significant. We did not observe a mean, RT median and RT variance significant interaction between ear and indicated that main effect of cycle over cycle (F (1,16)=.018, p=896). An REA was these data was not significant. 682 J.Neurol.Sci.[Turk] Table 4. Main Effect of Ear over Correct Answers of 17 Subjects in DL (verbal) Task during Two Phases CYCLE MENSTRUAL FOLLICULAR EAR Mean SD Mean SD RE 75.18 20.90 74.18 21.64 LE 30.35 18.93 29.06 17.67 Figure 4: Main Effect of Ear over Correct Answers of 17 Subjects in DL (verbal) Task during Two Phases Table 5. Main Effect of Cycle over Correct Answers (RE, LE) of 17 Subjects in DL (verbal) Task during Two Phases EAR RE LE CYCLE Mean SD Mean SD MENSTRUAL 75.18 20.90 30.35 18.93 FOLLICULAR 74.18 21.64 29.06 17.69 683 J.Neurol.Sci.[Turk] Figure 5: Main Effect of Cycle over Correct Answers (RE, LE) of 17 Subjects in DL (verbal) Task during Two Phase Table 6. Main Effect of Ear over RT Mean of 17 Subjects in DL (verbal) Task during Two Phases CYCLE MENSTRUAL FOLLICULAR EAR Mean SD Mean SD RE 1178.63 153.16 1152.01 178.77 LE 1239.22 167.95 1212.69 240.28 Figure 6: Main Effect of Ear over RT Mean of 17 Subjects in DL (verbal) Task during Two Phases 684 J.Neurol.Sci.[Turk] Mood 20 participants with confirmed P levels and Because cycle-dependent fluctuations in the 17 participants with confirmed E mood can affect interhemispheric levels. On the average they always showed processes(9), STCI-S18 was performed. We a clear REA and in most subtests, analyzed cheerfulness (CH), seriousness including a RT advantage for the right ear. (SE) and bad mood (BM) scores separately Thus, our technique to study language using ANOVA with the cycle phase as the asymmetry was successful. repeated measure. A significant effect of The results of the dichotic listening task cycle phase was not observed for the CH data showed that the degree of language (F (1,12)=2.04, p<.163, ns), SE (F asymmetry as revealed by dichotic (1,12)=1.13, p<1.98, ns) and BM (F listening did not change during the three (1,12)=.91, p<.41, ns) scores. First, we menstrual phases. We did find, however, conducted the analysis for the 12 that the main effect of cycle was participants whose E and P levels met our significant when we analyzed the data of criteria. Then, we repeated the same 17 participants with available E levels. analysis over the 17 participants with This result indicated that the total number available E levels and the 20 participants of correct responses (RE, LE) differed with available P levels. However, no between the menstrual and follicular significant main effect of cycle on the CH phases. But since we have not provided (F (1,17)=0.78, p<.39, ns), SE (F evidence for an interaction of asymmetry (1,17)=3.41, p<.08, ns) and BM (F with cycle phase, estradiol seems to affect (1,17)=.66, p<.43, ns) scores of 17 overall auditory recognition without participants with available E levels was altering language asymmetry. found. The result was similar for the 20 participants with available P levels in that REA is typical for right-handed the main effect of cycle on CH (F participants and indicates that more items (1,19)=0.510, p<.48, ns), SE (F are correctly reported from the right ear (1,19)=.850, p<.37, ns) and BM (F when compared to the left ear. Possibly, an (1,19)=.152, p<.70, ns) scores was not REA reflects the linguistic specialization of the left hemisphere(23)significant. . An REA has been reported to be a result of hemisphere DISCUSSION superiority in the processing of language- (28) In the current study, we investigated the related materials . Similar findings have change in cerebral asymmetry related to been confirmed by many DL studies(3,23,26,27,33,38)hormonal fluctuations during the menstrual . When speech sounds cycle by means of a verbal dichotic are presented, the DL task reveals an REA listening task. Although obtaining stable that highly correlates with the WADA-(25) asymmetries with a superiority of the right test . The perception and the production ear, we did not see alterations of this of the syllables are known as functions that lateralization with respect to estradiol or are associated with the laterality of (5,24,34) progesterone. LH . A recent study with a trial-by-trial analysis of event related potentials Verbal Dichotic Listening Task could reveal that the overall REA is a time- Throughout our analysis, we obtained a bound effect, which can be explained by stable right ear advantage (REA). A REA the late transfer of syllabic information (1) was observed using accuracy data from 12 from the right to the left hemisphere . The participants with confirmed P and E levels. results of the current study are in The same significant result was also accordance with the results of these obtained with the analysis performed using previous studies. 685 J.Neurol.Sci.[Turk] In previous studies, a change in the callosum does not simply exert excitatory asymmetry of the numbers of right and left or inhibitory action on the contralateral ear responses during cycle phases were hemisphere, but rather induces brief shown(37,42,41,12). We could not replicate glutamate-mediated excitatory this finding. This was clearly not related to postsynaptical potentials (EPSPs), mood effects which were carefully followed by a prolonged GABA-mediated controlled by additional tests. The present inhibition (IPSP). Progesterone suppresses study differs from previous studies because in a dose dependent fashion the glutamate- we also studied the RT as a dependent induced excitatory responses of neurons by variable. We indicated that the main effect about 87%,(39). Thus, the release of of ear over RT mean was significant when progesterone would result in a decrease of we analyzed the data of 17 participants non-NMDA glutamate receptor with available E levels and 20 participants responsiveness. Due to the reduction of with available P levels, separately. corticocortical transfer, a reduction of However, also in this variable we did not functional cerebral asymmetries see a change of asymmetry over the cycle. follows(20). Thus, neither accuracy nor speed measures could show that language asymmetries as So then, why was the effect size of our measured with dichotic listening are study so small? It is possible that it is subject to menstrual cycle changes. related to the unusual property of callosal fibers that connect the auditory cortical Negative findings are always more difficult fields and that are possibly involved in the to interpret than positive ones. Certainly generation of dichotic listening effect(1). the most important limitation of our study LaMantia and Rakic(29) revealed that the is the sample size. However, this resulted axons crossing between the auditory from the fact that we used very strict cortical areas are unusually large and criteria for subject inclusions and therefore heavily myelinated to possibly ensure exclude many women. This could in exceptionally fast conduction speed. It is principle result in a Type II error. With a possible that this anatomically distinct larger sample size, it might be possible to callosal pathway is less prone to be indicate an interaction of menstrual cycle modified by hormonal fluctuations. By and ear. combining several large data sets of (12) However, also a larger sample size would subjects as in Cowell et al. , this effect not increase the effect size. Due to this then becomes significant. This is not so in small effect size, only very large samples cases like the present one that utilizes can reveal an interaction of hormones and highly selected and thus smaller subject asymmetry changes in dichotic listening. numbers. Taken this issue into account, it The theory on progesterone dependent will likely be possible to get a clearer variation of cerebral asymmetry(19) picture in the future studies investigating assumes that hormones change brain the change of FCAs during menstrual asymmetry by altering cortico-cortical cycle. interactions. This cortico-cortical Acknowledgement: This work was interaction via the corpus callosum is supported partly by grant from Deutscher primarily mediated by glutamatergic fibers Akademischer Austausch Dienst (DAAD) that mostly synapse on AMPA and NMDA and the Commission of Scientific Research receptors on pyramidal neurons in the Projects of Uludağ University, Project other hemisphere. These pyramidal number: F(Y)-2009/2. neurons subsequently activate inhibitory GABAergic interneurons which induce a widespread inhibition. Thus, the corpus 686 J.Neurol.Sci.[Turk] Correspondence to: 7. Chiarello C, McMahon MA and Schaffer K. Handan Can Visual cerebral lateralization over phases of the menstrual cycle: A preliminary E-mail: Handancan@uludag.edu.tr investigation. Brain Cogn 1989, 11: 18–36. 8. Compton RJ and Levine SC. Menstrual cycle phase and mood effects on perceptual asymmetry. Brain Cogn 1997, 35: 168-183. 9. Compton RJ and Mintzer DA. 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