9-16 Language Networks

cortical regions

what are processing hubs and need to talk to each other?

subcortical regions

what relay sensory information to the cortex?

decomposes that sensory info (spoken & written language)

after subcortical regions send sensory information to cortex, what does the cortex do?

white matter tracts

how to cortical regions talk to each other?

neurological model

Carl Wernicke created what in 1874 but drew it in the right hemisphere and was revamped by Norman Geschwind

Wernicke-Geshwind obsolete language processing model

1. To hear, speech is sent through auditory pathway to Heschl’s gyrus, then to Wernicke’s area where word meaning is extracted

2. To speak, word meanings are sent from Wernicke’s area to Broca’s area. The model proposed Broca held representations of words. That information is sent to the motor cortex, then to the facial motor neurons in the brainstem to move facial muscles

3. To read, written text is sent from occipital lobe to the angular gyrus, then to Wernicke’s area (for silent reading) and then to Broca’s (for reading aloud

speech understanding and speech production

Although outdated, the Wernicke-Geshwind model was an important early milestone because it introduced the idea that language relies on a connecting nerve pathway between _______, paving the way for today's view of complex brain networks.

white matter

what are bundles of myelinated axons that connects cortical and subcortical regions (structural wiring of the brain)

gray matter

what are neuron cell bodies?

the cables that connect cortical processing hubs

white matter tracts

diffusion tensor imaging

what can you measure white matter pathways with? (measures directionality of water diffusion along axons)

1. Arcuate fasciculus

2. Superior longitudinal fasciculus

3. Uncinate fasciculus

4. Inferior fronto-occipital fasciculus; inferior longitudinal fasciculus

5. Frontal aslant tract

6. Corpus callosum

major white matter tracts in language (6)

Arcuate fasciculus

White matter tract that…

-Classic tract is identified in the Wernicke-Geschwind model

-Connects posterior temporal (Wernicke’s) and frontal (Broca’s) language regions

-Central to the dorsal stream*

-Exact functional contribution is still actively debated

superior longitudinal fasciculus

white matter tract that…

-Broader dorsal pathway connecting frontal, parietal, and temporal regions

-Overlaps functionally with arcuate fasciculus

Uncinate fasciculus

white matter tract that…

-Connects anterior temporal lobe to the frontal lobe

-Part of the ventral semantic pathway

Inferior fronto-occipital fasciculus and inferior longitudinal fasciculus

white matter tract that…

-Long ventral tracts linking occipital and temporal regions to the frontal lobe

-IFOF: Implicated in semantic processing and reading

-ILF: processes visual signals, helps with object and face recognition

frontal aslant tract

white matter tract that…

-More recently characterized

-Connects supplementary motor area(SMA)/pre SMA to Broca’s area

-Implicated in speech initiation and fluency (Stuttering research)

corpus callosum

white matter tract that…

-is a major interhemispheric tract

-Bilateral coordination of language processing

dual stream model of language

current prevailing model of speech processing

ventral, dorsal

two streams in dual stream model of language

how the dual stream works

the auditory cortex performs spectrotemporal analysis by breaking down raw sound into basic features like pitch, rhythm, and frequency, which the phonological network then organizes into recognizable speech units like syllables and phonemes. Once these speech sounds are identified, the signal splits into two distinct processing pathways to handle either understanding their meaning or coordinating the motor actions needed to repeat them.

phonological network

Linked system of brain regions along the superior temporal sulcus that process speech sounds, turning them from sounds into meaningful units (Also turn thoughts into spoken word). its activated by language tasks that require access to phonological information (speech perception and production)

ventral stream

stream that turns sound to meaning. (comprehension) responsible for speech comprehension by mapping raw acoustic speech sounds into concepts and vocabulary stored in the brain. there are two key anatomical networks

lexical interface

anatomical network in ventral stream that acts as a dictionary link between word sounds (phonology) and their meanings (semantics) (words and definitions). the brain regions include posterior middle temporal gyrus (pMTG) and posterior inferior temporal sulcus (pITS)

combinatorial network

anatomical network in ventral stream where makes individual words into larger semantic phrases and syntactic structures (grammar and sentences). the brain regions include anterior middle temporal gyrus (aMTG) and anterior inferior temporal sulcus (aITS)

uncinate fasciculus, inferior fronto-occipital fasciculus, inferior longitudinal fasciculus

white matter tracts that physically support the ventral stream for speech processing (critical for semantic processing and comprehension)

dorsal stream

stream that turns sound to articulation (production) it connects the sensory auditory system directly with the motor system, allowing the brain to convert heard speech sounds into motor plans for speech production. the pathway relies on network made up of posterior inferior frontal gyrus, and premotor cortex

insula

hidden region of the cortex that lies deep within the lateral fissure (sylvian fissure)

anterior insula

which part of the insula is involved in the dorsal stream pathway?

arcuate fasciculus, superior longitudinal fasciculus

white matter tracts that support the dorsal stream (critical for speech production and repetition)

ventral

if someone has difficulties with speech perception, which stream is likely impacted?

dorsal

Damage to the supramarginal gyrus or the arcuate fasciculus in the ____ stream causes conduction aphasia, where a person can speak smoothly and understand language, but cannot repeat back words or phrases exactly as heard.

frontal aslant tract damage

damage linked to initiation deficits, studied in relation to stuttering

cortical region

damage to white matter often produces more selective, dissociable deficits than damage to a single ______ alone

white matter

what helps conceptualize language processing as a network, and not just isolated to a “center”