Stimulation of female genital regions produces strong activation of various brain sites

A new study published in The Journal of Sexual Medicine reveals that for the first time, stimulation of the vagina, cervix, or clitoris was shown to activate three separate and distinct sites in the sensory cortex.

 

Some sexuality experts have claimed that the major source of genital sensation is from the clitoris, with relatively little sensation produced by vaginal or cervical stimulation.

Researchers led by Barry R. Komisaruk, B.S., Ph.D., of Rutgers University, used functional magnetic resonance imaging (fMRI) to map sensory cortical responses to clitoral, vaginal, cervical, and nipple self-stimulation in 11 healthy women, ages 23-56. For points of reference on the homunculus (also referred to as the “point-to-point body map” or a diagram showing where nerves from different parts of the body are represented in the brain) researchers also mapped responses to stimulation of the thumb and great toe.

Results found that stimulation of each of these genital regions in fact produces a significant and strong activation of specific and different sites in the sensory cortex.

The three representations are clustered in the same sensory cortical region as the genitals of men on the homunculus.

Nipple self-stimulation activated not only the chest region of the homunculus as expected, but also surprisingly the genital region of the sensory homunculus, suggesting a neurological basis for women’s reports that nipple stimulation feels erotic.

“Our findings demonstrate undeniably that there is a major input to the sensory cortex in response to stimulation of not only the clitoris, but of the vagina and cervix as well, which also evidently receive a significant and substantial sensory nerve supply,” Komisaruk concludes. “This lays the groundwork for an understanding of how genital stimulation spreads sequentially through the brain from initial activation of the sensory cortex to eventually activate the brain regionsthat produce orgasm.”

Irwin Goldstein, editor-in-chief of The Journal of Sexual Medicine, further explained the enormous significance of this ground breaking sexual medicine research. “In the 1930’s-1950’s, researchers localized in the brain exactly where all sensations in man were represented, including male genitalia. Data regarding location of clitoral sensation were only studied in 2010, some sixty years later. This current study in The Journal of Sexual Medicine reveals, for the first time, brain sensation localization data not only from the clitoris, but from the vagina, cervix and nipples. Being able to demonstrate the multiple locations in the brain where stimulation of different female genital regions are represented and how these brain locations inter-relate helps us to better understand women’s sexual function.”

 

The above story is reprinted (with editorial adaptations by MedicalXpress staff) from materials provided by Wiley (news : web)

Right or Left? Brain Stimulation Can Change Which Hand You Favor

When the left posterior parietal cortex of the brain received magnetic stimulation, right-handed volunteers were more likely to use their left hand to perform simple one-handed tasks, UC Berkeley research shows. (left; Credit: Image courtesy of Flavio Oliveira)

 

Each time we perform a simple task, like pushing an elevator button or reaching for a cup of coffee, the brain races to decide whether the left or right hand will do the job. But the left hand is more likely to win if a certain region of the brain receives magnetic stimulation, according to new research from the University of California, Berkeley.

UC Berkeley researchers applied transcranial magnetic stimulation (TMS) to the posterior parietal cortex region of the brain in 33 right-handed volunteers and found that stimulating the left side spurred an increase in their use of the left hand.

The left hemisphere of the brain controls the motor skills of the right side of the body and vice versa. By stimulating the parietal cortex, which plays a key role in processing spatial relationships and planning movement, the neurons that govern motor skills were disrupted.

“You’re handicapping the right hand in this competition, and giving the left hand a better chance of winning,” said Flavio Oliveira, a UC Berkeley postdoctoral researcher in psychology and neuroscience and lead author of the study, published in the journal Proceedings of the National Academy of Sciences.

The study’s findings challenge previous assumptions about how we make decisions, revealing a competitive process, at least in the case of manual tasks. Moreover, it shows that TMS can manipulate the brain to change plans for which hand to use, paving the way for clinical advances in the rehabilitation of victims of stroke and other brain injuries.

“By understanding this process, we hope to be able to develop methods to overcome learned limb disuse,” said Richard Ivry, UC Berkeley professor of psychology and neuroscience and co-author of the study.

At least 80 percent of the people in the world are right-handed, but most people are ambidextrous when it comes to performing one-handed tasks that do not require fine motor skills.

“Alien hand syndrome,” a neurological disorder in which victims report the involuntary use of their hands, inspired researchers to investigate whether the brain initiates several action plans, setting in motion a competitive process before arriving at a decision.

While the study does not offer an explanation for why there is a competition involved in this type of decision-making, researchers say it makes sense that we adjust which hand we use based on changing situations. “In the middle of the decision process, things can change, so we need to change track,” Oliveira said.

In TMS, magnetic pulses alter electrical activity in the brain, disrupting the neurons in the underlying brain tissue. While the current findings are limited to hand choice, TMS could, in theory, influence other decisions, such as whether to choose an apple or an orange, or even which movie to see, Ivry said.

With sensors on their fingertips, the study’s participants were instructed to reach for various targets on a virtual tabletop while a 3-D motion-tracking system followed the movements of their hands. When the left posterior parietal cortex was stimulated, and the target was located in a spot where they could use either hand, there was a significant increase of the use of the left hand, Oliveira said.

Other coauthors of the study are Jörn Diedrichsen from University College London, Timothy Gerstner from the University of Pittsburg and Julie Duque from the Université Catholique de Louvain in Belgium.

The study was funded by the Natural Sciences and Engineering Research Council of Canada, the Canadian Institutes of Health Research, the National Institutes of Health, the National Science Foundation and the Belgian American Educational Foundation.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of California — Berkeley.

Journal Reference:

Flavio T. P. Oliveira, Jörn Diedrichsen, Timothy Verstynen, Julie Duque, Richard B. Ivry. Transcranial magnetic stimulation of posterior parietal cortex affects decisions of hand choice. Proceedings of the National Academy of Sciences, 2010; DOI: 10.1073/pnas.1006223107

Interaction With Neighbors: Neuronal Field Simulates Brain Activity

Voltage-sensitive dye imaging across the surface of visual cortex revealed propagating activity waves which may be conveyed by long horizontal neuronal connections. (Credit: Image courtesy of Ruhr-Universitaet-Bochum)

The appearance of a spot of light on the retina causes sudden activation of millions of neurons in the brain within tenths of milliseconds. At the first cortical processing stage, the primary visual cortex, each neuron thereby receives thousands of inputs from both close neighbors and further distant neurons, and also sends out an equal amount of output to others. In recent decades, individual characteristics of these widespread network connections and the specific transfer characteristics of single neurons have been widely derived. However, a coherent population model approach that provides an overall picture of the functional dynamics, subsuming interactions across all these individual channels, is still lacking.

RUB Scientists of the Bernstein Group for Computational Neuroscience developed a computational model which allows a mathematical description of far reaching interactions between cortical neurons. The results are published in the open-access journal PLoS Computational Biology.

Cortical activity waves and their possible consequences for visual perception

By means of fluorescent dye that reports voltage changes across neuronal membranes it has been shown how a small spot of light, presented in the visual field, leads to initially local brain activation followed by far distant traveling waves of activity. At first, these waves remain sub-threshold and hence, cannot be perceived consciously. However, a briefly following elongated bar stimulus leads to facilitation of the initiated activity wave. Instead perceiving the bar at once in its full length, it appears to be drawn-out from the location of the previously flashed spot. In psychology this phenomenon has been named ‘line-motion illusion’ since motion is perceived even though both stimuli are displayed stationary. Thus, brain processes that initiate widespread activity propagation may be partly responsible for this motion illusion.

Neural Fields

RUB Scientists around Dr. Dirk Jancke, Institut für Neuroinformatik, have now successfully implemented these complex interaction dynamics within a computational model. A so-called neural field was used in which the impact of each model neuron is defined by its distant-dependent interaction radius: close neighbors are strongly coupled and further distant neurons are gradually less interacting. Two layers one excitatory, one inhibitory, are recurrently connected such that a local input leads to transient activity that emerges focally followed by propagating activity. Therefore, the entire field dynamics are no longer determined by the sensory input alone but governed to a wide extent by the interaction profile across the neural field. Consequently, within such a model, the overall activity pattern is characterized by interactions that facilitate distant pre-activation far away from any local input.

Such pre-activation may play an important role during processing of moving objects. Given that processing takes time starting from the retina, the brain receives information about the external world with a permanent delay. In order to counterbalance such delays, pre-activation may serve a “forewarning” of neurons that represent locations ahead of an object trajectory and thus, may enable a more rapid crossing of firing thresholds to save important processing times.

What can we generally learn from such a field model regarding brain function? Neural fields allow for a mathematical framework of how the brain operates beyond a simple passive mapping of external events but conducts inter-“active” information processing leading, in limit cases, to what we call illusions. The future challenge will be to implement neural fields for more complex visual stimulus scenarios. Here, it may be an important advantage that this model class allows abstraction from single neuron activity and provides a mathematically handy description in terms of interactive cortical network functioning.

Provided by Ruhr-Universitaet-Bochum, via AlphaGalileo.

Journal Reference:

Olaf Sporns, Valentin Markounikau, Christian Igel, Amiram Grinvald, Dirk Jancke. A Dynamic Neural Field Model of Mesoscopic Cortical Activity Captured with Voltage-Sensitive Dye Imaging. PLoS Computational Biology, 2010; 6 (9): e1000919 DOI: 10.1371/journal.pcbi.1000919