Speech & Language Networks

Receptive language

Auditory and reading comprehension

Expressive language

Spoken and written expression

Auditory comprehension of language

1. ear converts acoustic energy into electrochemical energy and transmits it to the brainstem via cranial nerve VIII

2. The brainstem sends this information to the thalamus

3. The thalamus relays the information to the primary auditory cortex (A1=BA41/BA42) for signal processing

4. A1 routes to Wernicke’s area (BA22) for meaning attachment

5. Wernicke’s area projects to Broca’s area (BA44/BA45) for higher-level syntactical processing

Auditory comprehension of language cont.

• 2 dorsal pathways (blue & purple)

  • Auditory-to-motor mapping via SLF

  • Syntax processing of complex sentences via AF

• 2 ventral pathways (pink & grey)

  • Semantic and basic syntactic processing via Inferior frontooccipital fasciculus & Uncinate fasciculus

Visual comprehension of language (reading)

1. Visual information is projected to the thalamus (green in picture, under BA 41/42) via the optic tracts

2. Thalamus projects to the occipital lobe’s visual areas (BA 17– 19) for visual processing via the optic radiations (geniculocalcarine tract)

3. The visual areas project a dorsal stream of vision (i.e., the “where” of vision) and a ventral stream of vision (i.e., the “what” of vision). When reading, the anterior, parietotemporal, and occipitotemporal reading systems activate

The oral production of language

1. Desire and thoughts to communicate originate in the prefrontal cortex and are sent to Broca’s area for language encoding and speech planning

2. Broca’s area projects to the supplementary motor area (SMA; top of area 6), which activates speech plans

3. SMA relays now active plans to the primary motor cortex

4. Primary motor cortex sends plans to the speech muscles for execution

Neural basis of speech

• Motor plan => motor program

  • Plan: high-level representation: the abstract sequence of movements needed to produce a specific utterance, before the execution begins.

  • Program: the detailed set of muscle-specific instructions that are carried out to execute the motor plan.

• Involved in execution of motor program

  • Motor pathways (descending) - Direct & Indirect pathway

  • Sensory pathways (ascending)

Neural basis of speech cont.

• Direct (pyramidal) pathway

  • Corticobulbar/corticospinal

  • Voluntary system

  • Control of gross motor movement

• Indirect (extrapyramidal) pathway

  • Involuntary movements - Posture, muscle tone, reflexes, movement modulation

  • Motor control circuits - Basal ganglia & Cerebellum

Initiation and executive of speech involves minimal network of speech production’

• motor areas, premotor areas, cerebellum, basal ganglia

The written expression of language

1. Desire and thoughts originate in the prefrontal cortex, which is sent to Broca’s area for language encoding

2. Language-encoded thoughts sent to premotor cortex (BA 6) for handwriting motor planning

3. Motor plans sent to the primary motor cortex

4. Primary motor cortex sends writing motor plans to the dominant hand

5. The superior parietal lobe coordinates the visuospatial elements of writing