The thalamus, coined from the Greek word for "chamber", thálamos, is the part of the brain responsible for signal relaying and prioritization. It consists of twin bulb-shaped regions, the thalami, symmetrical about the brain's midline. They are so close to the center of the brain that they occasionally interconnect, but typically don't. The thalamus is part of the limbic system, the region of the brain largely associated with the emotions.
The thalamus is best known as the final relay station for perceptual data before it is passed on to the cerebral cortex. It receives input from diverse brain areas, primarily including all the senses except olfaction. It is also responsible for regulating motor control.
The sensory apparatus of the human body registers a tremendous amount of information, far more information than can be put to good use. The thalamus joins a series of other machinery whose purpose is to distill sensory information into a more interpretable and manageable form for higher brain sections. The thalamus is engaged in an intimate relationship with the cerebral cortex, with numerous mutual connections. These connections make up the thalamacortical loop.
Because the thalamus is the nucleus of so much relaying activity, it has long been regarded as the Rosetta stone of the nervous system, giving a lot of insight into the importance and direction of various neural signals. The thalamus also modulates arousal mechanisms, maintains alertness, and directs attention to sensory events.
The thalamus consists of three circuits: the specific nucleii, the reticular formation, and the intralaminar circuit. The specific nucleii are responsible for scanning the cerebral cortex and determining active brain regions, those firing at around 40Hz, then relaying this information to the rest of the thalamus. The reticular formation is constantly making intelligent guesses as to what sensory object is generating these activation patterns. The intralaminar circuit compares these pattern guesses with similar patterns in memory. All these circuits cooperate to produce a coherent framework for the interpretation of incoming sensory data.
