Thalamus

• Schematic division of thalamic nuclei

  1. Thalamus

  2. Anterior

  3. Medial

  4. Lateral group
• Anterior group of nuclei

  • Enclosed by the bifurcation of the internal medullary lamina
• Medial group of nuclei

  • Consists of the medial nucleus, the midline nucleus, centromedian and the intralaminar nucleus
• Lateral group of nuclei

  • Further divided into dorsal and ventral nuclear groups
• Dorsal nuclear group


  • Contains lateral posterior nucleus, lateral dorsal nucleus and pulvinar
• Ventral nuclear group


  • Comprised of ventral anterior, ventral lateral and ventral posterior nuclei, and medial and lateral geniculate bodies
• Ventral posterior group


  • Also known as ventrobasal complex, consists of ventroposterolateral and ventroposteromedian groups of nuclei
• Physiologically there are four groups of nuclei

  • Specific relay nuclei
  • Association nuclei
  • Non-specific nuclei
  • Motor nuclei
• Specific relay nuclei

  • Ascending afferent inputs synapse on these nuclei, axons arising from them transmit the afferent impulse to cortex
• Ventrobasal complex (VBC)


  • Receives inputs from dorsal column pathway, anterolateral system and corticothalamic fibers, and projects to somatosensory cortex
• Trigeminal lemniscus


  • Carries the general sensations from face along with the gustatory afferents and project to the ventral posterior (VP) nucleus that transmits the afferent inputs to the postcentral gyrus
• Lateral geniculate body (LGB)


  • Receives input from optic tract and projects to visual cortex
• Medial geniculate body (MGB)


  • Receives input from auditory pathway and projects to auditory cortex
• Anterior nucleus


  • Receives inputs from the hypothalamus through the mammillothalamic tract and relays the information to the cingulate gyrus
• Association nuclei


  • Receive inputs from sensory cortex and limbic system and project diffusely to the association cortex or to sub-cortical structures
• Pulvinar


  • Projects to the inferior parietal lobe
• Dorsolateral nucleus


  • Reciprocally connected to the precuneate gyrus
• Non-specific nuclei


  • Include intralaminar (IM), midline, centromedian (CM) nuclei, and reticular nuclei (RET)
• Non-specific nuclei


  • Receive inputs mainly from reticular formation and paleospinothalamic tract, and also inputs from striatum, hypothalamus and other thalamic nuclei
• Non-specific nuclei


  • Project diffusely to wide areas of cerebral cortex, to thalamus and limbic system
• Motor nuclei


  • Include lateral, ventral anterior and ventral lateral nuclei
• Ventral lateral nucleus


  • Receives input from the cerebellum through the dentato-rubro-thalamic tract and projects to the motor cortex area 4 and 6
• Ventral anterior nucleus


  • Receives inputs from basal ganglia and projects to the premotor cortex
• Extrinsic nuclei


  Specific relay nuclei
• Intrinsic nuclei


  Rest of the thalamic nuclei
• All somatosensory information reaches all of these different types of thalamic nuclei
• Functions of Thalamus


  • Relay station for all somatic sensations
  • Relay of special sensations
  • Arousal mechanisms
  • Subcortical Perception of Sensations
  • Motor Functions
  • Memory and Emotion
  • Synchronization of EEG
  • Role in Sleep
  • Sensory Motor Coordination
  • Language and Speech
• Relay station for all somatic sensations


  • Thalamus conveys the sensory information to the cortex through thalamocortical projections
• Relay of special sensations

  • Thalamus is the relay center for all special sensations except olfaction
• Arousal mechanisms


  • Thalamocortical projects from nonspecific nuclei to cortex contributes to reticular activating system that activates arousal mechanisms and keeps the individual awake
• Subcortical Perception of Sensations

  • Subcortical perception of pain, temperature, pressure (crude touch) occurs to some extent in thalamus
• Motor Functions


  • Thalamus is an integral part of motor loop of the brain, influences postural movements, and links cerebellum and motor cortex
• Memory and Emotion


  • Anterior thalamus is a constituent of Papez circuit, concerned with recent memory and emotion
• Synchronization of EEG


  • Stimulation of intralaminar thalamic nuclei at low frequency causes synchronization of EEG waves, high frequency stimulation causes arousal and desynchronization
• Role in Sleep


  • Thalamocortical loop is important in generating the pattern of brain activity in sleep-wake cycle, inhibitory thalamic reticular neurons are proposed to be part of this network that causes induction of sleep
• Sensory Motor Coordination


  • Thalamus receives all sensory inputs from the body and closely interacts with basal ganglia, cerebellum and motor cortex, therefore is one of the major structures for coordination between sensory and motor functions
• Language and Speech


  • Dorsal lateral nucleus of thalamus is reciprocally connected with parietal lobe, concerned with language and speech and complex integrated functions