Neuroanatomy & Neurophysiology for Speech Production

Primate Vocalization Circuit

This circuit builds on other circuits for producing learned voluntary vocalizations, including speech. It involves neural pathways connecting the auditory cortex, frontal cortex, and the brainstem, facilitating the complexity of vocal communication.

Reticular Formation

A set of interconnected nuclei in the brainstem that play a crucial role in regulating arousal, attention, and some aspects of vocalization.

Brainstem area

Where is the reticular formation area in the brain?

Final convergence zone

What projection zone from higher level brain areas are used for vocalization and helps coordinate muscle movement for muscles for vocalization (e.g., respiratory, laryngeal, orofacial).

Reticular Formation

This area receives projections from the cortex and modulates sensory information and motor functions, influencing arousal and attention.

Limbic pathway

A neural pathway that connects the limbic system to other brain regions, playing a key role in emotion and memory regulation. Serves a gating function that allows commands from the cortex to reach the brainstem and influence physiological responses via the reticular formation

Intensity; loudness

The limbic pathway controls _____ of the vocalization, NOT _____ part.

Gating system

This system in the limbic system represents motivation or readiness to vocallze. y

Motor control pathway

Responsible for production of learned vocalization, including higher-level coordination of the muscles for vocalizing

Direct Activation Pathway

A neural pathway that facilitates the direct control of voluntary speech movements, supporting rapid and precise vocalizations. Connects the motor cortex to lower motor neurons via the corticobulbar and corticospinal tracts.

Red nucleus

A structure in the brainstem involved in motor coordination, particularly in controlling limb movements and interacting with the cerebellum. It is a group of neurons in the midbrain

Reticular Formation and Red Nucleus

These nuclei in the brain stem receive input from the corticorubral tract (to the red nucleus) and corticoreticular tracts

Reticular Formation

What area may help coordinating vocal fold movement for speech and in an affective (emotional) prosody?

Indirect

Is the reticular formation and red nucleus part of the direct or indirect pathway for speech motor control?

• Reflexes

• Muscle tone

The reticular formation and red nucleus plays a modulatory role and lesions to this indirect pathway affect mostly what 2 things?

Pyramidal tract

What is the direct activation pathway also called?

Extrapyramidal system

What is the indirect activation pathway also called?

90%

What % of the direct activation pathway cross at the level of the medulla?

Corticobulbar tracts

Bundles of axons that transmit motor commands from the brain’s cortex to the cranial nerve nuclei

Corticospinal tracts

Bundles of axons that transmit motor commands from the brain’s cortex to the spinal nerves

Lateral corticospinal tract

This is when 90% of the corticospinal tracts cross at the level of the medulla

Anterior corticospinal tracts

This is when 10% of the corticospinal tracts don’t cross at the level of the medulla

Periaqueductal Gray Matter (PAG)

This is a midbrain structure that surrounds the cerebral aqueduct and acts as a gating signal to modulate precisely timed motor commands of learned vocalizations from the motor cortex- affects intensity and timing

Emotional vocalizations

The PAG stimulates motor commands for what?

• Intensity

• Timing

The PAG affects what 2 things in learned vocalizations.

Mutism

Bilateral PAG lesion can result in WHAT?

Thalamus

This is a relay station for information entering or leaving the cerebral cortex

Which ventral lateral nucleus is important for speech?

Left

Ventral Posterior Medial Nucleus

This projects to somatosensory cortex

Medial Geniculate Nucleus

Relays information from auditory brainstem to the auditory cortex (involved in relaying hearing information)

Ventral Anterior Nucleus

Connects with the premotor cortex

• Ventral Anterior Nucleus

• Ventral Lateral Nucleus

What 2 ventral nuclei form part of the portico-basal ganglia and portico-cerebellar loop?

• Caudate Nucleus

• Putamen

• Globus Pallidus

What is the series of basal ganglia structures?

Caudate Nucleus

Wraps around the thalamus and plays a crucial role in motor and cognitive functions (e.g., planning and executing movements, learning, memory, reward processing, etc.)

Putamen

Lateral to the thalamus and is in charge of reward processing, motor control, and other cognitive functions

Globus pallidus

External and internal - lateral to thalamus

Stratum

Refers to caudate and putamen

Lentricular nucleus

Refers to the putamen and globus pallidus

• Substantia nigra

• Subthalamic nucleus

• Reticular formation (a brainstem structure)

What are some important connections to other areas that we can consider to be apart of the basal ganglia?

Reticular Formation

Mediates ascending sensory information, integrates sensorimotor information, has complex effects on LMNs

Huntington’s Disease

What disease has damage to the basal ganglia leading to an increase in muscle tone extremities and is intrinsically excitatory?

Parkinson’s Disease

What disease has damage to the basal ganglia leading to reduced muscle tone and isn’t intrinsically excitatory

•Regulates muscle tone

•Adjusts associated movements (arm swing, facial expression)

•Suppresses extraneous movements

•Facilitates wanted/voluntary movements

•Deals with mood and personality

The basal ganglia modulates cortical movement commands in several different ways such as:

Basal Ganglia Function

•Motor relay and integrating system. Most motor pathways run through here

•Plays a large role in automatic movement and motor learning

•Chooses between alternative motor programs

•Sends a gating signal to activate chosen program and inhibit competing program

Direct Pathway

What pathway of the basal ganglia facilitates movement?

Indirect pathway

What pathway of the basal ganglia inhibits movement?

Prefrontal circuit

May be involved in buffering and sequencing of speech sounds in multisyllabic utterances

Cingulate circuit

May be involved in the will to speak and affective (emotional) prosody

Ataxia

What is found in cerebellar damage and these individuals sound drunk?

•Muscle synergy – muscles working together

•Coordination and smoothness in time and space

•Muscle tone

•Movement range

•Movement strength

Equilibrium (and resistance to gravity)

The cerebellum contributes to several functions such as:

•Compares efferent and afferent signals

•Important for motor learning

•Error control device

What are some other aspects that the cerebellum is in control of?

Cerebellum

• Regulates movements (particularly rapid, alternating, and sequential movements)

• Signals to (sensory) and from (motor to LMNs) the cerebellum are ipsilateral (same side)

Inferior cerebellar peduncles

This connects the medulla to the cerebellum and most signals from the body sent to the cerebellum are done here

Middle cerebellar peduncles

This connects the pons with the cerebellum and signals from the motor cortex sent to the cerebellum are done here

Superior cerebellar peduncles

This connects the midbrain with the cerebellum and motor fibers leave the cerebellum after analysis and go to the thalamus and motor cortex

Predictive (feedforward) control form one movement to the next

The cerebellum is required for adapting what?

Sylvian fissure

Fissure around the temporal lobe

Rolandic fissure

Fissure on top of one’s head

• Vocalizations

• Repetitions of words or syllables

• Speech arrest

• Slowing of speech

• Hesitancy

Stimulation of the supplemental motor areas can yield:

Transient period of total mutism followed by possible decline in self-initiated speech with automatic speech intact (transcortical motor aphasia)

Lesions in the supplemental motor area leads to what?

Dorsal to pons and medulla

Where is the cerebellum located?

Medial frontal lobe

Where is the cingulate (limbic system) motor area?

Cingulate motor areas

Higher-order motor areas in the cortex, located within the cingulate sulcus next to the primary and supplementary motor cortices

Akinetic mutism

Bilateral damage to the cingulate motor area can result in what?

Akinetic mutism

Near complete lack of speech and general lack of movement despite normal arousal and intact sensory, motor, and cognitive functions

Posterior to ventral postcentral gyrus in inferior parietal lobe

Where is the supra marginal gyrus located?

Supramarginal gyrus

•Phonological store for verbal working memory (words you are holding onto while speaking)

•Contains somatosensory error cells that represent the difference between expected and actual sensation during speech.

Control of speech

Somatosensory feedback is based on what?

• Opercularis

• Orbitalis

• Triangularis

What are the 3 regions to the inferior frontal gyrus?

Inferior Frontal Gyrus

What is involved in speech motor control and suggests portions of posterior IFG act as a link between phonology and speech motor control

• Inferior frontal gyrus pars opercularis

• Inferior frontal gyrus pars triangularis

What 2 regions are apart of Broca’s area?

Inferior frontal gyrus pars orbitalis

What region of the inferior frontal gyrus has a strong connectivity with the auditory cortex and superior temporal gyrus and sulcus?

Insula

•Integrates a wide range of cognitive, motor, somatosensory and auditory info

•Strong connections (structural – connections with axons - and functional) with surrounding portions of IFG, Rolandic cortex, superior temporal gyrus and

•Strong functional connectivity with preSMA and cingulate motor area

• Type of speech task

• Complexity

• Other factors

There are conflicting studies of the insula’s role in speech due to what types of factors?

Auditory cortical areas

What does the superior temporal cortex contain?

Sylvian fissure

The primary auditory cortex in Heschl’s gyrus is within what fissure?

• Rolandic cortex

• Insula

Posterior superior temporal gyrus (pSTG) and HG are strongly structurally and functionally connected with what 2 things?

Auditory feedback

What can be used to fix speech?

Auditory error map

Represents mismatches between efferent and afferent signals during speech (connects what we say to what we wanted to say)

Left posterior superior temporal cortex = Wernicke’s area

These connections make sense as we hear what we say; but covert speech also activates aud. Cortex –copies of motor commands from motor cortical regions are sent to aud. Cortex. (whether spoken aloud or not)