Brain areas involved in speech production.

ability to produce accurate speech sounds in rapid succession is something we humans take for granted. In fact, speech production is an extremely involved process. Thoughts must be translated into linguistic representations (itself not a trivial feat), which are then sent to speech mechanisms that can coordinate, initiate, modify and execute the articulation of an utterance. Through the study of patients with disorders affecting this complex process, we have come to learn that numerous brain areas are recruited in speech production and that they hang in a precarious balance that is easily affected by neurological disease and dysfunction. The coordination of articulatory movements, an end-stage component of speech production, has received increased attention in recent years. In order for sounds to be produced correctly, the lips, tongue, jaw, velum and larynx must make accurate movements at the right time or the intended sounds become distorted. For example, to say the simple word`gap,' air¯ow must brie¯y be halted by raising the back of the tongue to the soft palate. This air¯ow is suddenly released, during which time the vocal cords must vibrate to create phonation. The tongue and jaw lower and the air should ¯ow unobstructed to produce the proper vowel. The lips seal and the cords relax. All of this must be orchestrated perfectly in time and sequence so that the word`gap' results. Given the many ®ne movements that are required for speech production, it is no wonder that the mouth area is so largely represented in the homunculus of primary motor cortex. Patients with de®cits in this ability to programme speech movements are said to have a disorder known asàpraxia of speech'. The disorder has been well studied in the realm of speech±language pathology, and treatment for the disorder has received equal attention (Wertz et al., 1984; Duffy, 1995; McNeil et al., 1997). The brain regions that might support this function had been less well investigated until the advent of neuroimaging techniques that allowed for the in vivo investigation of the brain areas affected in patients who had sustained injuries that resulted in apraxia of speech. In one such study (Dronkers, 1996), the computer-reconstructed lesions of 25 chronic stroke patients with left hemisphere lesions who had been diagnosed with apraxia of speech were overlapped to determine if a common area of infarction could be found in this group. The only region of overlap in 100% of the cases was …