Broca’s Area (Inferior Frontal Gyrus)

Anatomy

• Pars opercularis (BA 44) and pars triangularis (BA 45) of the inferior frontal gyrus.
• Language is lateralized to the left hemisphere in about 95% of right-handers and ~70% of left-handers.
• Connected to Wernicke’s area by the arcuate fasciculus and superior longitudinal fasciculus.
• Blood supply: superior division of the MCA.

Functions

• Motor planning of speech and articulatory sequencing.
• Syntax and processing of complex sentence structures.
• Verbal working memory (phonological loop — articulatory rehearsal).
• Semantic selection and word retrieval (BA 45).
• Imitation and action understanding (mirror neuron system, BA 44).
• Right IFG: response inhibition (the “stop” signal), emotional prosody.

Connections and chemistry

• Wernicke’s area (arcuate fasciculus — dorsal language stream)
• Premotor cortex / SMA
• Basal ganglia (speech initiation)
• Right IFG → subthalamic nucleus (hyperdirect inhibitory pathway)

Development

Developmental course through childhood and adolescence.

• Myelination of the arcuate fasciculus is weak at birth and increases through childhood.
• Maturation of complex syntactic processing extends into the school years.
• After early left-hemisphere injury, language can shift to the right hemisphere (early plasticity).

Clinical

• Developmental language disorder (DLD): about 7.6% in a screening of 7,267 children at school entry (two children in every class of 30); language disorder associated with intellectual disability or a medical diagnosis adds another 2.3% (Norbury et al., 2016). Structural and functional differences in the left IFG. Common but under-recognized; may be mistaken for an attention or behavior problem. A
• Stuttering: differences in the left IFG and related white matter tracts, overactivation in the right hemisphere.
• ADHD: right IFG hypoactivation, difficulty with response inhibition.
• Tourette syndrome: the right IFG as part of the inhibitory control networks.

Treatment

This region from the perspective of medication, psychotherapy and neuromodulation. Letter badges are evidence levels.

• In developmental language disorder: speech and language therapy; school support and classroom accommodations. Monitoring for reading difficulties and social-emotional problems.
• Preschool stuttering: the Lidcombe program (delivered by parents, praising fluent speech and gently correcting stuttering) in 54 children aged 3–6, the proportion of stuttered syllables at 9 months was 1.5% in the Lidcombe group and 3.9% in the control group (Jones et al., 2005). Supports early intervention. B
• Response inhibition in ADHD (right IFG): stimulants and atomoxetine increase right IFG activity; details on the STN and DLPFC cards. B

Assessment

Neuropsychological tasks and measures that probe this region's function.

• Letter fluency, Boston Naming Test
• Sentence repetition, grammar comprehension tests
• Stop-Signal and Go/No-Go tasks (right IFG)

Lesions and damage

Clinical findings expected with damage or dysfunction.

• Broca’s aphasia: nonfluent, telegraphic speech, agrammatism; comprehension relatively spared, repetition impaired.
• Apraxia of speech, writing impairment.

In the model

How this structure is defined in the 3D model, and the data source.

HCP-MMP1.0 areas (Glasser et al., 2016; MNI volumetric version: Horn, 2016) 44 and 45; inferior frontal sulcus areas go to the DLPFC, frontal operculum areas follow the CerebrA gyrus.

References

Full citations for the card; links go to the paper (DOI) or a PubMed search.

1. Norbury CF et al. The impact of nonverbal ability on prevalence and clinical presentation of language disorder: evidence from a population study. J Child Psychol Psychiatry 2016;57:1247–1257. Search PubMed
2. Jones M et al. Randomised controlled trial of the Lidcombe programme of early stuttering intervention. BMJ 2005;331:659. Search PubMed