cerebral ventricles The cerebral ventricles are a series of interconnected chambers deep inside the brain, filled with cerebrospinal fluid (CSF). The two largest, the lateral ventricles, are located symmetrically in each cerebral hemisphere; each has three culs de sac or ‘horns’, extending into the frontal, temporal and occipital lobes. The lateral ventricles of the two sides are linked by the interventricular foramen and they are connected through paired openings (foramina of Monro) to the single centrally placed third ventricle, for which the corpus callosum is the roof and the thalamus forms the flanking walls. The third ventricle communicates via a narrow canal (the aqueduct of Sylvius) through the centre of the midbrain with the fourth ventricle which lies behind the lower part of the brain stem. The ventricles each contain a choroid plexus that secretes cerebrospinal fluid.

The ventricles were observed by the influential Hellenistic physician and anatomist, Galen of Bergama (129–216 ad) and became known as ‘cells’. They were the central feature of a theory of brain function that was endorsed by the medieval philosophers and Fathers of the Christian Church, and which remained dominant until the eighteenth century. The clear fluid within the cells, which was thought to be a distillate of blood and inhaled air, was called ‘animal spirit’ (from the Latin anima: ‘mind’), because it was supposed to be the seat of behavioural and mental functions. Information carried by nerves from the sense organs was said to enter the fluid of the first cell (the lateral ventricles), where it gave rise to sensations. This cell communicated with the middle cell (the third ventricle), which was responsible for ‘imagination’ and ‘estimation’, and the fluid then passed into the final cell (the fourth ventricle), which was concerned with memory and the control of movement. Although this hypothesis is, of course, totally discredited, it is interesting that it was essentially mechanistic (rather than mystical) and it incorporated a principle that is clearly established by modern neuroscience, namely that the nervous system processes sensory information to provide the basis of thoughts, memories, and actions.

Laurence Garey, and Colin Blakemore

See also brain; cerebrospinal fluid; hydrocephalus.