The Major Thalamic Nuclei
It's that time of the month (no- not the one you're thinking of) where I go on a scientific rant that maybe two people will relate to/ find useful, but it's more as a way for me to practice writing out "short answer"questions for my Neuro exam tomorrow. :3
So yeah, if you're potentially curious about some of the groups of cells
in the thalamus that basically allow us to live, experience our environment, and be conscious, then read onward!
Many Neuroscientists think of the thalamus (latin for "chamber/ room") is the geographic center of the brain (at least my Professor who's testing us tomorrow does). There are two thalami, connected by an intermediate mass (which contains no axons and is purely a structural bridge between the two hemispheric thalami), surrounding by a prominent "fan" of axon fibers known as the internal capsule, which eventually merges into the corona radiata of the cortex. These axon fibers carry information flowing to and from the thalamus, though in all honesty, the conversation between the thalamus and the cortex is largely a one-sided one (with the cortex doing most of the talking).
Below I've summarized the major thalamic nuclei (this list is certainly not exhaustive, nor are the sub-descriptions for each nucleus) and their functions (at least what we know of them in today's current field). dy
1) Sensory Bodies (the Medial Geniculate Body and the Lateral Geniculate Nucleus)
- MGB --> projects to auditory cortex (A1, or Area 41)
- LGN --> projects to visual cortex (V1, or Area 17)
- Not very prominent in the human thalamus, though much larger in "lower" organisms (i.e. rodents)
2) Pulvinar (Polymodal Association Nucleus)
- Very prominent in human thalamus (about 40% of the weight), considered polymodal because it performs three distinct functions
- Lateral/ inferior pulvinar --> projects to superior colliculus (visual attention)
- Oral pulvinar --> projects to somatosensory cortex
- Medial pulvinar --> projects to "emotion"/ limbic cortical regions (i.e. cingulate gyrus)
- Lesions of this region can result in attention deficit/ neglect disorders (much like lesions to the parietal lobe)
3) Somatosensory Thalamus (the VPL and the VPM)
- VPL --> receives inputs from dorsal column/ anterolateral spinal pathways (epicritic and protopathic respectively)
- VPM --> receives trigeminal afferents (from main trigeminal nucleus and spinal trigeminal pathways)
4) Intralaminar Nuclei (the "Reticular Formation" of the Thalamus)
- Group of nuclei that play a crucial (but "non-specific") role in governing attention, awareness, learning, and consciousness in the cortex
- The Centromedian is thought to play a critical role in consciousness, as bilateral lesions cause vegetative state/ coma. Often grouped with the Parafascicularis as the "CM-Pf"
- NOTE: A band of grey matter often grouped with the Basal Ganglia, the Claustrum, has recently been shown to also play a role in the on/off switch nature of consciousness
5) Medial Group/ Nuclei
- Play important role in olfaction, pain sensation, and emotions (project to the olfactory cortex, the somatosensory cortex and cingulate gyrus)
6) Lateral Group/ Nuclei (the "Limbic" Thalamus)
- Receive inputs from limbic structures (i.e. the hippocampus/ amygdala), play a role in processing and relaying emotion information
- Considered connected with the anterior nuclei (integrating limbic and motor behaviors)
7) Motor Thalamus (VLc and VLo)
- VLc (pars caudalis) receives cerebellar input (from dentate nucleus of cerebrocerebellum)
- VLo (pars oralis) receives basal ganglia inputs
- Involved in integrating motor information from basal ganglia and cerebellum with cortical motor execution (Areas 6 and 4)
8) Anterior Nuclear Group
- Integrates motor and limbic information (projects to orbitofvrontal cortex + cingulate gyrus)
- Grouped with lateral (limbic) nuclei due to it's proximity
9) Reticular Nucleus of the Thalamus
- A shell of GABAergic neurons that surrounds the thalamus, participates in the thalamacorticoreticulothalamic circuit (say that 10 times fast :3)
- Cortex --> Reticular Nucleus --> Thalamus --> Cortex