Instruct: Given a question, retrieve relevant passages that can help answer the question.
Query: What area of the cortex controls speech?
Broca's area or the Broca area /broʊˈkɑː/ or /ˈbroʊkə/ is a region in the frontal lobe of the dominant hemisphere, usually the left, of the brain[1] with functions linked to speech production.
The first areas of the brain to be pruned are those involving primary functions, such as motor and sensory areas. The areas of the brain involved in more complex processes lose matter later in development. These include the lateral and prefrontal cortices, among other regions. Some of the most developmentally significant changes in the brain occur in the prefrontal cortex, which is involved in decision making and cognitive control, as well as other higher cognitive functions. During adolescence, myelination and synaptic pruning in the prefrontal cortex increases, improving the efficiency of information processing, and neural connections between the prefrontal cortex and other regions of the brain are strengthened. This leads to better evaluation of risks and rewards, as well as improved control over impulses. Specifically, developments in the dorsolateral prefrontal cortex are important for controlling impulses and planning ahead, while development in the ventromedial prefrontal cortex is important for decision making. Changes in the orbitofrontal cortex are important for evaluating rewards and risks.
A motor plan state can be assumed for representing a motor plan, i.e. the planning of speech articulation for a specific syllable or for a longer speech item (e.g. word, short phrase). This state map is assumed to be located in the premotor cortex, while the instantaneous (or lower level) activation of each speech articulator occurs within the primary motor cortex (see motor cortex).
The frontal lobe contains the precentral gyrus and prefrontal cortex and, by some conventions, the orbitofrontal cortex. These three areas are represented in both the left and the right cerebral hemispheres.The precentral gyrus or primary motor cortex is concerned with the planning, initiation and control of fine motor movements dorsolateral to each hemisphere. The dorsolateral part of the frontal lobe is concerned with planning, strategy formation, and other executive functions. The prefrontal cortex in the left hemisphere is involved with verbal memory while the prefrontal cortex in the right hemisphere is involved in spatial memory. The left frontal operculum region of the prefrontal cortex, or Broca's area, is responsible for expressive language, i.e. language production. The orbitofrontal cortex is concerned with response inhibition, impulse control, and social behaviour.
Auditory sensory memory has been found to be stored in the primary auditory cortex contralateral to the ear of presentation. This echoic memory storage involves several different brain areas, due to the different processes it is involved in. The majority of brain regions involved are located in the prefrontal cortex (PFC) as this is where the executive control is located, and is responsible for attentional control. The phonological store and the rehearsal system appear to be a left-hemisphere based memory system as increased brain activity has been observed in these areas. The major regions involved are the left posterior ventrolateral prefrontal cortex (VLPFC), the left premotor cortex (PMC), and the left posterior parietal cortex (PPC). Within the VLPFC, Broca's area is the main location responsible for verbal rehearsal and the articulatory process. The dorsal PMC is used in rhythmic organization and rehearsal, and finally the PPC shows a role in localizing objects in space.
The precentral cortex is an area of the frontal cortex that is located directly anterior to the central sulcus and includes both the primary motor cortex and the supplementary motor area. Inputs that project to both of these areas arise from a variety of locations in the brain that integrate sensory stimuli including the primary motor cortex, the thalamus and corticospinal projections. These two areas along with several other main functional areas control both the preparation of motor movement as well as the execution of movements. These main functional areas are crucial to the development of the motor related symptoms associated with frontal lobe epilepsy focally when seizures are located within these defined areas. The major functional areas include:
The left opercular part of the inferior frontal gyrus is a part of the articulatory network involved in motor syllable programs. The articulatory network also contains the premotor cortex, and the anterior insula. These areas are interrelated but have specific functions in speech comprehension and production. The articulatory network acts mostly when the vocal tract moves to produce syllables. The pars opercularis acts indirectly through the motor cortex to control the motor aspect of speech production, and codes motor programs for this system, while the auditory cortex (via the temporoparietal junction in the lateral sulcus (Sylvian fissure) houses a series of sensory targets. Together, these areas function as a sensory-motor loop for syllable information coding.
Despite the views of Penfield and Woolsey, a consensus emerged that area 4 and area 6 had sufficiently different functions that they could be considered different cortical fields. Fulton helped to solidify this distinction between a primary motor cortex in area 4 and a premotor cortex in area 6. As Fulton pointed out, and as all subsequent research has confirmed, both primary motor and premotor cortex project directly to the spinal cord and are capable of some direct control of movement. Fulton showed that when the primary motor cortex is damaged in an experimental animal, movement soon recovers; when the premotor cortex is damaged, movement soon recovers; when both are damaged, movement is lost and the animal cannot recover.
There are several organic and psychological factors that can affect speech. Among these are:The classical or Wernicke-Geschwind model of the language system in the brain focuses on Broca's area in the inferior prefrontal cortex, and Wernicke's area in the posterior superior temporal gyrus on the dominant hemisphere of the brain (typically the left hemisphere for language). In this model, a linguistic auditory signal is first sent from the auditory cortex to Wernicke's area. The lexicon is accessed in Wernicke's area, and these words are sent via the arcuate fasciculus to Broca's area, where morphology, syntax, and instructions for articulation are generated. This is then sent from Broca's area to the motor cortex for articulation.
Many of the areas Brodmann defined based solely on their neuronal organization have since been correlated closely to diverse cortical functions. For example, Brodmann areas 3, 1 and 2 are the primary somatosensory cortex; area 4 is the primary motor cortex; area 17 is the primary visual cortex; and areas 41 and 42 correspond closely to primary auditory cortex. Higher order functions of the association cortical areas are also consistently localized to the same Brodmann areas by neurophysiological, functional imaging, and other methods (e.g., the consistent localization of Broca's speech and language area to the left Brodmann areas 44 and 45). However, functional imaging can only identify the approximate localization of brain activations in terms of Brodmann areas since their actual boundaries in any individual brain requires its histological examination.
The sensory areas are the cortical areas that receive and process information from the senses. Parts of the cortex that receive sensory inputs from the thalamus are called primary sensory areas. The senses of vision, audition, and touch are served by the primary visual cortex, primary auditory cortex and primary somatosensory cortex respectively. In general, the two hemispheres receive information from the opposite (contralateral) side of the body. For example, the right primary somatosensory cortex receives information from the left limbs, and the right visual cortex receives information from the left visual field. The organization of sensory maps in the cortex reflects that of the corresponding sensing organ, in what is known as a topographic map. Neighboring points in the primary visual cortex, for example, correspond to neighboring points in the retina. This topographic map is called a retinotopic map. In the same way, there exists a tonotopic map in the primary auditory cortex and a somatotopic map in the primary sensory cortex. This last topographic map of the body onto the posterior central gyrus has been illustrated as a deformed human representation, the somatosensory homunculus, where the size of different body parts reflects the relative density of their innervation. Areas with lots of sensory innervation, such as the fingertips and the lips, require more cortical area to process finer sensation.
New medical imaging techniques such as PET and fMRI have allowed researchers to generate pictures showing which areas of a living brain are active at a given time. In the past, research was primarily based on observations of loss of ability resulting from damage to the cerebral cortex. Indeed, medical imaging has represented a radical step forward for research on speech processing. Since then, a whole series of relatively large areas of the brain have been found to be involved in speech processing. In more recent research, subcortical regions (those lying below the cerebral cortex such as the putamen and the caudate nucleus) as well as the pre-motor areas (BA 6) have received increased attention. It is now generally assumed that the following structures of the cerebral cortex near the primary and secondary auditory cortices play a fundamental role in speech processing:The left hemisphere is usually dominant in right-handed people, although bilateral activations are not uncommon in the area of syntactic processing. It is now accepted that the right hemisphere plays an important role in the processing of suprasegmental acoustic features like prosody.
The motor control for speech production in right handed people depends mostly upon areas in the left cerebral hemisphere. These areas include the bilateral supplementary motor area, the left posterior inferior frontal gyrus, the left insula, the left primary motor cortex and temporal cortex. There are also subcortical areas involved such as the basal ganglia and cerebellum. The cerebellum aids the sequencing of speech syllables into fast, smooth and rhythmically organized words and longer utterances.
The primary auditory cortex is surrounded by secondary auditory cortex, and interconnects with it. These secondary areas interconnect with further processing areas in the superior temporal gyrus, in the dorsal bank of the superior temporal sulcus, and in the frontal lobe. In humans, connections of these regions with the middle temporal gyrus are probably important for speech perception. The frontotemporal system underlying auditory perception allows us to distinguish sounds as speech, music, or noise.
The prefrontal cortex is located in the most anterior portion of the frontal lobe in the brain. It forms a larger portion of the cortex in humans. The dendrites in the prefrontal cortex contain up to 16 times as many dendritic spines as neurons in other cortical areas. Due to this, the prefrontal cortex integrates a large amount of information. The orbitofrontal cortex cells are important factors for self-control. If an individual has the choice between an immediate reward or a more valuable reward which they can receive later, an individual would most likely try to control the impulse to take that immediate reward. If an individual has a damaged orbitofrontal cortex, this impulse control will most likely not be as strong, and they may be more likely to take the immediate reinforcement. Additionally, we see lack of impulse control in children because the prefrontal cortex develops slowly.
Functional imaging finds that the shadowing of nonwords occurs through the dorsal stream that links auditory and motor representations of speech through a pathway that starts in the superior temporal cortex, goes to the inferior parietal cortex and then the posterior inferior frontal cortex (Broca's area).
Vogt and Vogt in 1919 also suggested that motor cortex was divided into a primary motor cortex (area 4) and a higher-order motor cortex (area 6) adjacent to it. Furthermore, in their account, area 6 could be divided into 6a (the dorsal part) and 6b (the ventral part). The dorsal part could be further divided into 6a-alpha (a posterior part adjacent to the primary motor cortex) and 6a-beta (an anterior part adjacent to the prefrontal cortex). These cortical fields formed a hierarchy in which 6a-beta controlled movement at the most complex level, 6a-alpha had intermediate properties, and the primary motor cortex controlled movement at the simplest level. Vogt and Vogt are therefore the original source of the idea of a caudal (6a-alpha) and a rostral (6a-beta) premotor cortex.
Somatotopy is the point-for-point correspondence of an area of the body to a specific point on the central nervous system. Typically, the area of the body corresponds to a point on the primary somatosensory cortex (postcentral gyrus). This cortex is typically represented as a sensory homunculus which orients the specific body parts and their respective locations upon the homunculus. Areas such as the appendages, digits, penis, and face can draw their sensory locations upon the somatosensory cortex. The areas which are finely controlled (e.g., the digits) have larger portions of the somatosensory cortex whereas areas which are coarsely controlled (e.g., the trunk) have smaller portions. Areas such as the viscera do not have sensory locations on the post central gyrus.
Speech production is process by which a thought in the brain is converted into an understandable auditory form. This is a multistage mechanism that involves many different areas of the brain. The first stage is planning, where the brain constructs words and sentences that turn the thought into an understandable form. This occurs primarily in the inferior frontal cortex, specifically in an area known as Broca's area. Next, the brain must plan how to physically create the sounds necessary for speech by linking the planned speech with known sounds, or phonemes. While the location of these associations is not known, it is known that the supplementary motor area plays a key role in this step. Finally, the brain must signal for the words to actually be spoken. This is carried out by the premotor cortex and the motor cortex.
In most cases, speech production is controlled by the left hemisphere. In a series of studies, Wilder Penfield, among others, probed the brains of both right-handed (generally left-hemisphere dominant) and left-handed (generally right-hemisphere dominant) patients. They discovered that, regardless of handedness, the left hemisphere was almost always the speech controlling side. However, it has been discovered that in cases of neural stress (hemorrhage, stroke, etc.) the right hemisphere has the ability to take control of speech functions.
Two cortical processing streams exist: a ventral one which maps sound onto meaning, and a dorsal one, that maps sound onto motor representations. The dorsal stream projects from the posterior Sylvian fissure at the temporoparietal junction, onto frontal motor areas, and is not normally involved in speech perception. 
Carl Wernicke identified a pathway between the left posterior superior temporal sulcus (a cerebral cortex region sometimes called the Wernicke's area) as a centre of the sound "images" of speech and its syllables that connected through the arcuate fasciculus with part of the inferior frontal gyrus (sometimes called the Broca's area) responsible for their articulation. This pathway is now broadly identified as the dorsal speech pathway, one of the two pathways (together with the ventral pathway) that process speech. The posterior superior temporal gyrus is specialized for the transient representation of the phonetic sequences used for vocal repetition. Part of the auditory cortex also can represent aspects of speech such as its consonantal features.
Eloquent cortex is a name used by neurologists for areas of cortex that—if removed—will result in loss of sensory processing or linguistic ability, minor paralysis, or paralysis. The most common areas of eloquent cortex are in the left temporal and frontal lobes for speech and language, bilateral occipital lobes for vision, bilateral parietal lobes for sensation, and bilateral motor cortex for movement. 
Attentional control refers to an individual's capacity to choose what they pay attention to and what they ignore. It is also known as endogenous attention or executive attention. In lay terms, attentional control can be described as an individual's ability to concentrate. Primarily mediated by the frontal areas of the brain including the anterior cingulate cortex, attentional control is thought to be closely related to other executive functions such as working memory.
The Betz cells, or giant pyramidal cells in the primary motor cortex, are sometimes mistaken to be the only or main output from the cortex to the spinal cord. This mistake is old, dating back at least to Campbell in 1905. Yet the Betz cells compose only about 2-3% of the neurons that project from the cortex to the spinal cord, and only about 10% of the neurons that project specifically from the primary motor cortex to the spinal cord. A range of cortical areas including the premotor cortex, the supplementary motor area, and even the primary somatosensory cortex, project to the spinal cord. Even when the Betz cells are damaged, the cortex can still communicate to subcortical motor structures and control movement. If the primary motor cortex with its Betz cells is damaged, a temporary paralysis results and other cortical areas can evidently take over some of the lost function.
The neurological pathway of voluntary exhalation is complex and not fully understood. However, a few basics are known. The motor cortex within the cerebral cortex of the brain is known to control voluntary respiration because the motor cortex controls voluntary muscle movement. This is referred to as the corticospinal pathway or ascending respiratory pathway. The pathway of the electrical signal starts in the motor cortex, goes to the spinal cord, and then to the respiratory muscles. The spinal neurons connect directly to the respiratory muscles. Initiation of voluntary contraction and relaxation of the internal and external internal costals has been shown to take place in the superior portion of the primary motor cortex. Posterior to the location of thoracic control (within the superior portion of the primary motor cortex) is the center for diaphragm control. Studies indicate that there are numerous other sites within the brain that may be associated with voluntary expiration. The inferior portion of the primary motor cortex may be involved, specifically, in controlled exhalation. Activity has also been seen within the supplementary motor area and the premotor cortex during voluntary respiration. This is most likely due to the focus and mental preparation of the voluntary muscular movement.
Humans seem to have analogous anterior and posterior vocal pathways which are implicated in speech production and learning. Parallel to the avian posterior vocal pathway mentioned above is the motor cortico-brainstem pathway. Within this pathway, the face motor cortex projects to the nucleus ambiguous of the medulla, which then projects to the muscles of the larynx. Humans also have a vocal pathway that is analogous to the avian anterior pathway. This pathway is a cortico-basal ganglia-thalamic-cortico loop which begins at a strip of the premotor cortex, called the cortical strip, which is responsible for speech learning and syntax production. The cortical strip includes spans across five brain regions: the anterior insula, Broca’s area, the anterior dorsal lateral prefrontal cortex, the anterior pre-supplementary motor area, and the anterior cingulate cortex. This cortical strip has projections to the anterior striatum which projects to the globus pallidus to the anterior dorsal thalamus back to the cortical strip. All of these regions are also involved in syntax and speech learning.