Abstract
Transcranial direct current stimulation (tDCS) is a non-invasive method of modulating levels of cortical excitability. In this study, data gathered over a number of previously conducted experiments before and after tDCS, has been re-analyzed to investigate correlations between sex differences with respect to neuroplastic effects. Visual evoked potentials (VEPs), phosphene thresholds (PTs), and contrast sensitivity measurements (CSs) are used as indicators of the excitability of the primary visual cortex. The data revealed that cathodally induced excitability effects 10 min post stimulation with tDCS, showed no significant difference between genders. However, stimulation in the anodal direction revealed sex-specific effects: in women, anodal stimulation heightened cortical excitability significantly when compared to the age-matched male subject group. There was no significant difference between male and female subjects immediately after stimulation. These results indicate that sex differences exist within the visual cortex of humans, and may be subject to the influences of modulatory neurotransmitters or gonadal hormones which mirror short-term neuroplastic effects.
Highlights
In the human brain, the visual and motor cortices continue to be popular models for the investigation of induced structural plasticity in the adult brain, as their effects can be measured by visual ~VEPs and PTs! responses or motor evoked potentials ~MEPs!, respectively ~Nitsche & Paulus, 2000; Boroojerdi et al, 2002; Antal et al, 2004!
Kuo et al ~2006! recently reported sex differences in the primary motor cortex after short-duration tDCS; female subjects showed prolonged after-effects of cathodal stimulation, while male subjects showed stronger anodally-induced after effects
Previous animal and human studies of neuroplasticity and sex differences centered on cognitive functions ~Kimura, 2002; Juraska, 1998! where male and female populations are assessed for hormonal influences on cognitive functions ~spatial navigation facial processing emotion and memory; ~see Cahill, 2006 for review!!, which are believed to underlie these differences in cognitive responses between the sexes
Summary
The visual and motor cortices continue to be popular models for the investigation of induced structural plasticity in the adult brain, as their effects can be measured by visual ~VEPs and PTs! responses or motor evoked potentials ~MEPs!, respectively ~Nitsche & Paulus, 2000; Boroojerdi et al, 2002; Antal et al, 2004!. The visual and motor cortices continue to be popular models for the investigation of induced structural plasticity in the adult brain, as their effects can be measured by visual ~VEPs and PTs! Responses or motor evoked potentials ~MEPs!, respectively ~Nitsche & Paulus, 2000; Boroojerdi et al, 2002; Antal et al, 2004!. Recently reported sex differences in the primary motor cortex after short-duration tDCS; female subjects showed prolonged after-effects of cathodal stimulation, while male subjects showed stronger anodally-induced after effects. Previous animal and human studies of neuroplasticity and sex differences centered on cognitive functions ~Kimura, 2002; Juraska, 1998! Where male and female populations are assessed for hormonal influences on cognitive functions ~spatial navigation facial processing emotion and memory; ~see Cahill, 2006 for review!!, which are believed to underlie these differences in cognitive responses between the sexes.
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