IJCRR - 7(15), August, 2015
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IMPACT OF GENDER AND HEAD SIZE ON VISUAL EVOKED POTENTIALS
Author: Rubiya Shaikh, Rupali K. Parlewar
Abstract:The aim of the study is to compare head circumference in Gender and then to correlate head circumference with P100 latency, N75-P100 and P100-N145 amplitude. Visual evoked potentials are electrical potential differences recorded from scalp in response to visual stimuli. Numbers of factors that influence VEP waveforms include Age, Sex, Drugs, Head circumference. In the present study head circumference, P100 latency, N75- P100amplitude and P100 -N 145amplitude were recorded in 30 healthy males and 30 healthy females in the age group of 18-25 yrs. It is observed that head circumference is more in males. Also P100 latency is more in males as compared to females which is attributed to longer visual pathway. And amplitudes are larger in females as compared to males which is attributed to genetically determined sex differences in neuro-endocrinological systems. Present study also shows positive correlation between head circumference and latency and negative correlation between head circumference and amplitude. When the latency and amplitude of both males and females of same head circumference (53-55cm) were compared it was found that latency does not show significant results. But amplitude is more in female which is attributed to genetically determined sex
differences in neuro-endocrinological systems.
Keywords: Visual evoked potential, Head circumference, P100 latency, N75-P100 amplitude, P100-N145 amplitude
Visual evoked potentials are electrical potential differences recorded from scalp in response to visual stimuli (1).Visual evoked potentials (VEPs) are used to interrogate the visual pathway from the retina up through high-level visual cortices(2).
Numbers of factors that influence VEP waveforms include Age, Sex, Drugs, Head circumference (1). Gender is presumed to be one of the factors causing inter-individual variability in the brain’s electrophysiological parameter (2).the P100 latency is longer in adult males as compared to females. This has been attributed to larger head size and lower core body temperature in males (3). The mean P100 amplitude is greater in females compared to males (1).
Not many studies carried out showing how significantly these parameters affect VEP. Hence an attempt has been made, to correlate how gender has impact on VEPs, So that these factors will be considered clinically while recording VEP. The aim of the study is to compare head circumference in Gender and then to correlate head circumference with P100 latency, N75-P100 and P100-N145 amplitude.
MATERIALS AND METHODS
The study was conducted in a Grant Govt Medical College and J J Hospitals in Mumbai with the prior permission of the Dean of the institute and the ethical committee. 60 Healthy subjects males (n=30), females (n=30).Within in the age group of 18-25 years were subjected to a series of tests exercising utmost care in conduction so as to achieve the maximum possible accuracy with the available setup. A brief explanation to subjects regarding the procedure was given and voluntary informed consent of the subjects was taken.
The subjects selected were having no, medical, neurological and ophthalmic problems. The subjects were not on any medication likely to affect or influence VEPs or drugs affecting moods (antidepressant, tranquilizers). Prior to the study all subjects completed a healthy history questionnaire and a medical examination.
Visual function tests were done. Head circumference was measured in cm. Pattern reversal VEP was done on NeuroMEP machine. The low cut filters (LF) are set at 2 Hz and high cut filters (HF) are set at 100 Hz. Electrode impedance set at < 5kΩ. Active electrode applied at midline 4cm above inion (Oz). Reference electrode applied at 12 cm above nasion (Fpz) and ground electrode at vertex (Cz).P100 latency and N75- P100 amplitude and P100 - N145 amplitude were recorded. Pearson’s Correlation Coefficient (r) was used for Correlation of Head circumference with VEP. Student’s t test –was used for analysis of VEP in Gender.
It is observed that head circumference in males is significantly more than female. Also the P100 latency and N75- P100 amplitude and P100- N 145amplitude show significant values. There is positive correlation between head circumference and latency. Increase in head circumference also increases latency. And negative correlation between head circumference and amplitude. Increase head circumference decreases amplitude.
Significant positive correlation between Head circumference and Latency is suggestive of larger the head circumference, larger is brain size and longer conduction pathway and thus prolonging VEP latencies; as per Kothari et al (4).
Also as per Schmidt Neilsen K, the assumption that the anatomic variation is isometric, differences in all dimensions will be proportional and any pathway in brain will vary in length as cube root of brain volume (5)
If we take the VEP in males and females of having same range of head circumference (53-55) it is observed that latency does not show significant changes but amplitude show significant changes
Yasuhiro Kaneda et al (3)had concluded that, the large VEP amplitude, and the tendency for increased α power % and at LP verified in their study were considered to indicate that the VEP amplitude at LP reflects the effect of estrogen more than progesterone, and that the VEP latency and EEG changes at LP reflect the effect of progesterone more than estrogen. We believe that VEP analysis is a useful tool for the study of the actions of gonadal hormones on CNS, not only in animals but also in humans. And therefore Sex differences in VEPs (more Amplitude in females) may be attributed to genetically determined sex differences in neuro-endocrinological systems
Head circumference is significantly larger in males. P100 Latency in male is more than female; this is attributed to longer visual pathway. Also larger amplitude in females, is attributed to genetically determined sex differences in neuroendocrinological systems.
Head circumference has significant Positive correlation with latency and negative correlation with amplitude. Males and Females having same range of head circumference have no significant difference in Latency.
Authors acknowledge the immense help received from the scholars whose articles are cited and included in the references of this manuscript. Authors are also grateful to authors /editors /publishers of all those articles, journals and books from where the literature for this article has been reviewed and discussed.
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