1.   This view is strengthened by the fact that direct stimulation of the brain can produce sensory impressions in patients undergoing brain surgery.

2.   It was felt that high concentrations would be more likely to cause direct stimulation of the enteric endocrine cells and thus to be effective.

3.   And it would produce, through direct neural stimulation, a virtual reality indistinguishable from objective reality.

4.   All three work only in response to direct physical stimulation.

5.   Unlike the injection-style drugs, Viagra requires foreplay and direct stimulation in order to produce an erection, she said.