IV. Thalamic Afferent/Efferent Connections

A. Sensory Thalamus – Somatosensory & gustatory

• VPM

Afferent – Trigeminothalamic fibers (pain, temperature, touch from trigeminal nuclei); gustatory fibers (from nucleus solitarius).

Efferent – Primary somatosensory cortex (head and face areas in Brodmann’s areas 3,1,2); Post. Insular cortex (taste)

• VPL

Afferent – Anterolateral system (somatic pain and temperature)Dorsal column/medial lemniscus (somatic touch,

proprioception, deep pressure vibratory sense).

Efferent – Primary somatosensory cortex (body region in areas 3,1,2)

IV (Connections- cont.)

B. Motor Thalamus – Basal ganglia and cerebellar circuits.• VA

Afferent - Internal globus pallidus (GPi); pars reticulata of substantia nigra (SNr).Efferent – Premotor cortex (area 6).

• VLAfferent – GPi, SNr, cerebellar dentate nucleus.Efferent – Primary motor cortex (area 4)

IV (Connections – cont.)C. Limbic Thalamus – Cognition, emotions

• Ant and LD - formation of new memories)Afferent – mammillothalamic tract (from mammillary body).Efferent – cingulate gyrus.

• DM – affective behaviorsAfferent – Amygdala, hypothalamusEfferent – limbic cortex

D. Intralaminar thalamus

(CM-PF) – diffuse arousalAfferent – basal ganglia, cerebellum, ALS, reticular formation, cortex.

Efferent – basal ganglia, cortex.

IV (Connections – cont.)

E. Reticular – sets overall activity state of thalamus.

Afferent – other thalamic nuclei, cortex.

Efferent – other thalamic nuclei but not the cortex.

F. LP and Pulv - higher sensory cognitive function.

Afferent – brainstem visual, auditory centers, cortex

Efferent – areas 5, 7 (LP), Areas 18, 19 (Pulv).

G. MG and LG – metathalamus for audition and vision.

Afferent – inferior colliculus (MG), retina (LG).

Efferent – areas 41 and 42 (MG), area 17 (LG).

V. Effect of Focal LesionsA). VPM/VPL lesions

• Small tumors (irritating lesions) can produce intense pain on the contralateral head or body (sometimes both). This is called “thalamic pain” and can be triggered by a single somatosensory stimulus.

• Destructive (e.g, degenerative) lesions cause loss of somatic sensation on the contralateral head or body. ALS function returns but DC/ML function is permanently lost.

• Thalamic Syndrome. It is caused by severe damage to posterior thalamus, often including the adjacent internal capsule and basal ganglia. Symptoms include thalamic pain, hemianesthesia, sensory ataxia, hemiparesis and involuntary movements.

B). VA/VL lesions

• Lesions can elicit movement disorders that share characteristics of basal ganglia and cerebellar damage.

• Basal ganglia and cerebellar diseases result in dysregulated transmission within the motor thalamus

V. Effect of….(cont.)

C). Ant and DM lesions• Memory loss. Mammillothalamic input to Ant is part of a limbic system

loop that functions in the formation of new memories.• Loss of perception and affect. DM is connected to different components

of the limbic system. It is reciprocally connected with the prefrontal cortex functioning in affective behaviors and perception (foresight). Bilateral damage of DM has effects similar to prefrontal lobotomy.

D). Intralaminar thalamic lesions• Patient cannot maintain an aroused state.

E). Pulv lesions• Loss of visual attentiveness.