1. The Broca’s Area

1.1. What Is the Function of the Broca’s Area?

The main functions of Broca’s area are language production and comprehension that are controlled by different parts of Broca’s area [1].

Its role in language production is associated with the control of motor movements that allow for speech.

Its role in language comprehension is associated with its involvement in semantics (meaning of words) and phonology (sound of the words).

However, Broca’s area is also involved in the control of language repetition, sentence grammar and fluidity, gesture production, and the interpretation of others’ actions.

1.2. In What Part of the Brain Is the Broca’s Area?

The Broca’s area, also known as Brodmann’s area 44, is situated in the lateral frontal lobe of the dominant cerebral hemisphere, which is usually the left cerebral hemisphere.

It is limited anteriorly by the lateral Sylvian fissure which separates the frontal and parietal lobes, and posteriorly by the precentral gyrus found in the posterior part of the frontal lobe.

1.3. What Happens When the Broca’s Area Is Damaged?

Damage to the Broca’s area can be caused by brain injury, stroke, or brain tumors resulting from a partial loss in the capacity to produce spoken and written language, known as Broca’s aphasia (expressive aphasia).

2. The Wernicke’s Area

2.1. What Is the Function of the Wernicke’s Area?

The main function of Wernicke’s area is the control of phonologic retrieval without requiring semantic processing (meaning of words), auditory perception (sound), or speech articulation [2].

Phonological retrieval is the ability to recall the phonemes (the distinction between words) associated with specific graphemes (a group of letters representing a sound).

2.2. In What Part of the Brain Is the Wernicke’s Area?

The Wernicke’s area, also known as Brodmann area 22, is situated in the posterior temporal lobe of the dominant cerebral hemisphere (superior temporal gyrus), which is usually the left cerebral hemisphere. It is limited superiorly by the angular gyrus.

2.3. What Happens When the Wernicke’s Area Is Damaged?

Damage to the Wernicke’s area can be caused by brain injury, ischemia or stroke, brain tumors, abscesses, encephalitis, or seizures [3], resulting in fluent aphasia characterized by a correct ordering of words but with the lack of meaning of the produced phrases.

3. Angular Gyrus

3.1. What Is the Function of the Angular Gyrus?

The angular gyrus is involved in language and number processing, memory, and reasoning [4].

3.2. In What Part of the Brain Is the Angular Gyrus?

The angular gyrus, also known as Brodmann area 39, is a horseshoe-shaped structure situated in the inferior posterior parietal lobe.

It is limited superiorly by the intraparietal sulcus, posteriorly by the parieto-occipital sulcus, and anteriorly by the supramarginal gyrus.

3.3. What Happens When the Angular Gyrus Is Damaged?

Lesions (e.g., degeneration) to the angular gyrus result in symptoms such as alexia with agraphia, Gerstermann syndrome, and behavioral changes, including depression, poor memory, irritation, and aggressiveness [5].

Alexia is an impairment of writing and reading which can be associated or not with agraphia (loss of the capacity to communicate by writing).

Gestermann syndrome manifests with the inability to write (agraphia or dysgraphia), comprehend mathematics (acalculia or dyscalculia), distinguish right from left, and identify hand fingers (finger agnosia).

4. What Is a Speech and Language Disorder?

Speech and language disorders are disorders that affect the capacity of an individual to speak, listen, comprehend, read, and write. The following are the most common speech and language disorders:

• Aphasia
• Alalia
• Dysarthria
• Spasmodic Dysphonia
• Apraxia of Speech
• Lisping
• Stuttering
• Cluttering
• Muteness
• Speech Sound disorders

4.1. What Is Aphasia?

Aphagia is the lack of the capacity to comprehend and communicate through language [6].

4.1.1. Broca’s Aphasia

Broca’s aphasia is a partial loss in the capacity to produce spoken and written language due to lesions in Broca’s area caused by brain injury, stroke, or brain tumors.

4.1.2. Wernicke’s Aphasia

Wernicke’s aphasia is fluent aphasia characterized by a correct ordering of words but with the lack of meaning of the produced phrases.

It is caused by lesions in the Wernicke’s area that can be caused by brain injury, ischemia or stroke, brain tumors, abscesses, encephalitis, or seizures.

4.1.3. Global Aphasia

Global aphasia is when both the Broca’s area and the Wernicke’s area are damaged resulting in a loss of all aspects of speech and language.

4.1.4. Logopenic Primary Progressive Aphasia (lvPPA)

LvPPA is due to a generation of the angular gyrus resulting in slowed speech with normal articulation, and impaired naming of things, and comprehension of the syntax of sentences.

4.1.5. Primary Progressive Aphasia (PPA)

PPA is a progressive loss of speech and language associated with gradual degeneration of the Broca’s area, the Wernicke’s area, and the angular gyrus.

4.2. What Is Apraxia of Speech?

Apraxia of speech is the inconsistent production of speech sounds and rearranging of sounds in a word, such as “tomato” becoming “motamo”, that can be caused by a progressive illness, ischemia, or stroke.

4.3. What Is Dysarthria?

Dysarthria is characterized by the difficulty to speak due to weakness of speech muscles caused by nerve damage, injury, or stroke.

4.4. What Is Spasmodic Dysphonia?

Spasmodic Dysphonia is due to spasms affecting the vocal cords resulting in a shaky, raucous, or jittery voice which may be caused by an abnormal functioning of the brain basal ganglia [7].

4.5. What Is Alalia?

Alalia is commonly known as speech delay which may be due to slow development, hearing loss, intellectual disability, psychosocial deprivation, or autism.

4.6. What Is Lisping?

Lisping is characterized by distorted sounds due to incorrect positioning of the tongue in the mouth while speaking.

4.7. What Is Stuttering?

Stuttering is characterized by repetition or prolongation of sounds, words, or syllables, and speech interruptions. 

4.8. What Is Cluttering?

Cluttering is characterized by a rapid rate of speech which makes it difficult to understand.

4.9. What is Muteness?

Muteness is a disorder characterized by a complete inability to speak.

Conclusion

The 3 main areas of the brain that control speech and langue are the Broca’s area, the Wernicke’s area, and the angular gyrus. Damages that affect one or more areas result in speech and language problems.

The verity of the disorder can result in partial loss of certain aspects of speech or its complete loss which depends on the importance of the damage and the number of affected areas.

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