Area 44 and parts of area 45 in the left hemisphere make up our motor speech center. The area is often called Broca's field and is connected to the sensory speech center through an association pathway, the arch, fasciculus arcuatus. The task of the Motor Speech Center is to put together the movement programs required to formulate intelligible speech sounds. The programs are then delivered to the areas of SM I, which control the tongue, lips, throat, soft palate and vocal cords as well as respiratory, abdominal and pelvic muscles.
Area 44 and parts of area 45 in the right hemisphere are responsible for something called prosody, i.e. for the rhythm of speech, its melody, its emotional charge and dialect, and for singing.
An injury to Broca's field gives rise to so-called motor speech paralysis or Brocas-/motor-/expressive- aphasia.
Motor aphasia means that the affected person speaks slowly and laboriously searches for the words. The nouns and verbs used are pronounced in their simplest conceivable basic forms without inflections. Adjectives, adverbs, conjuctions, and prepositions are rarely used. A person suffering from motor aphasia can still understand both spoken and written language, but has great difficulty repeating spoken words. In severe cases, there is a pure inability to formulate intelligible speech sounds. Speech can then consist of forced, often short and monotonously repeated incomprehensible compositions of consonant and vowel sounds, sometimes with a mixture of profanity and power expressions.
It was precisely this more severe form of motor aphasia that the French neurologist Paul Broca studied in Paris in the mid-1800s. Broca was able, in 1861, to demonstrate the connection between motor aphasia and an injury at the back of the lower forehead in a stroke patient. After a reasonable recovery and until his death a few years later, he worked as an janitor at Broca's clinic. As permanent but after the impact there remained a total inability to intelligible speech. But he understood address and functioned in his chore. The only thing he uttered was something that sounded like.. Tan.. And every now and then something that sounded like slurred profanity. He was therefore called Monsieur Tan by Broca and has under that name taken his place in the history of medicine; This was the first time that the connection between a specific manifestation of the brain's work and a specific cortex area could be clearly demonstrated.
See also Phineas Gage!!