Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the major progestogen in the body. Progesterone has a variety of important functions in the body. It is also a crucial metabolic intermediate in the production of other endogenous steroids, including the sex hormones and the corticosteroids, and plays an important role in brain function as a neurosteroid.In addition to its role as a natural hormone, progesterone is also used as a medication, such as in combination with estrogen for contraception, to reduce the risk of uterine or cervical cancer, in hormone replacement therapy, and in feminizing hormone therapy. It was first prescribed in 1934. Biological activity
Progesterone is the most important progestogen in the body. As a potent agonist of the nuclear progesterone receptor (nPR) (with an affinity of KD = 1 nM) the resulting effects on ribosomal transcription plays a major role in regulation of female reproduction. In addition, progesterone is an agonist of the more recently discovered membrane progesterone receptors (mPRs), of which the expression has regulation effects in reproduction function (oocyte maturation, labor, and sperm motility) and cancer although additional research is required to further define the roles. It also functions as a ligand of the PGRMC1 (progesterone receptor membrane component 1) which impacts tumor progression, metabolic regulation, and viability control of nerve cells.
The Riddoch syndrome is a term coined by Zeki and Ffytche (1998) in a paper published in Brain. The term acknowledges the work of George Riddoch who was the first to describe a condition in which a form of visual impairment, caused by lesions in the occipital lobe, leaves the sufferer blind but able to distinguish visual stimuli with specific characteristics when these appear in the patients blind field. The most common stimuli that can be perceived consciously are the presence and direction of fast moving objects (moving at a speed in excess of 10 degrees per second); in his work these moving objects were described as "vague and shadowy". Riddoch concluded from his observations that "movement may be recognized as a special visual perception".Riddochs description was dismissed by Sir Gordon Holmes in a 1918 paper in which he wrote that" The condition described by Riddoch should not be spoken of as a dissociation of the elements of visual sensation" because "occipital lesions do not produce true dissociations of function with intact retinal sensibility". The idea of a separate representation of visual motion was further dismissed by H.L. Teuber  and, in general, such an idea was not accepted until physiological studies in the monkey demonstrated the existence of a cortical area lying outside the primary visual cortex (area V1) in which almost all cells were selective for directional motion.