Unable to figure out why you can't get to bed with her after several attempts while your closest friend is never short of offers? Your brain is simply not wired for sex.
According to a fascinating research, some people are actually wired to have more sex - or at least be really, really motivated to hook up.
"Some people's brains are simply more sensitive to sexual cues than others - which means it takes less to get them aroused and ultimately leads them to find sexual partners," explained Nicole Prause, an assistant research scientist in psychiatry at University of California Los Angeles.
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To prove their point, Prause and her team recruited psychology students to get an electroencephalogram (EEG) of their brains and to view 225 standardised pictures of pleasant, neutral or unpleasant things.
The pleasant images included sexually stimulating ones like explicit pictures of people having sex.
The students were also asked about their number of sexual partners in the past year.
Some of the participants showed strong reactions on the EEG to nearly all of the intimacy-themed images, regardless of whether they were explicit.
These were the same people who reported having more partners.
For these people, said Prause, it's not a chasing of a high or a reward but a biological sensitivity to sexual cues that sets their arousal threshold at a much lower level.
We may be wired to want sex, but that does not mean the wiring can't be re-routed, she said in the study published in the journal Social Cognitive and Affective Neuroscience.