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The thalamusA deep brain structure that relays and filters sensory information on its way to the cortex.Read more → matters because almost every sensory signal passes through it on the way to the cortex. Damage there can distort or block a specific sense entirely. It is a paired, egg-shaped structure deep in the brain that relays sensory information, with a different nucleus (cluster of neurons) handling each sense. For example, imagine a stroke that damages only the lateral geniculate nucleus: the patient loses vision in part of their visual field, while hearing and touch stay normal. In practice, knowing which thalamic nucleus handles which sense lets a clinician localise a lesion from the pattern of loss alone.

The thalamusA deep brain structure that relays and filters sensory information on its way to the cortex.Read more → relays almost all sensory information to the cortex, with one exception: smell (olfaction), which reaches the cortex more directly. The lateral geniculate nucleus relays visual information from the retina to the visual cortex, while the medial geniculate nucleus relays auditory (hearing) information from the ear to the auditory cortex. The mediodorsal nucleus connects to the prefrontal cortexThe front part of the brain responsible for planning, judgement and controlling impulses.Read more → and is important for memory; damage to it is implicated in Wernicke-Korsakoff syndromeA chronic memory disorder, usually from thiamine deficiency, marked by severe short-term memory loss and confabulation.Read more → (a memory disorder caused by thiamine deficiency). The thalamus is a distinct structure from the hypothalamusA small brain structure that controls basic functions like hunger, temperature, sleep and hormone release.Read more →, which sits just below it and controls hormones and basic drives such as hunger and temperature. Take a patient with chronic alcohol use who develops severe new memory loss: mediodorsal thalamic nucleus damage from thiamine deficiency is a recognised cause. In practice, distinguishing thalamic from hypothalamic damage matters, since one produces sensory or memory deficits and the other produces hormonal or drive disturbances.

• Two thalamic nuclei relay signals from the cerebellumThe brain structure at the back of the skull that coordinates balance and smooth movement.Read more → and basal gangliaA group of deep brain structures that help control movement and are affected in Parkinson's disease and by antipsychotic drugs.Read more → onward to the motor cortex. Which pair performs this motor relay function?
• The largest thalamic nucleus has extensive connections with association cortex and is implicated in directing visual attention. Which nucleus is this?
• A thin inhibitory shell of neurons surrounds the thalamusA deep brain structure that relays and filters sensory information on its way to the cortex.Read more →, sends no fibres to cortex, and is implicated in generating the spindles seen in light sleep. Which nucleus is this?
• Weeks after a small stroke, a man develops severe burning pain over the affected side, worsened by light touch. Damage to which thalamic region best explains this?

• Lateral geniculate nucleus, relays vision, unlike the medial geniculate nucleus which relays hearing.
• Thalamus, relays sensory information to the cortex, whereas the hypothalamusA small brain structure that controls basic functions like hunger, temperature, sleep and hormone release.Read more → controls hormones and basic drives.
• Mediodorsal nucleus, linked to memory via prefrontal connections, unlike the purely sensory geniculate nuclei.
• Smell (olfaction), the one sense that bypasses the thalamusA deep brain structure that relays and filters sensory information on its way to the cortex.Read more →, rather than being relayed like vision, hearing, and touch.

• Those nuclei serve memory and prefrontal functions instead.
• Those nuclei modulate thalamic activity rather than relaying motor signals.
• Those two nuclei relay vision and hearing respectively.
• The first relays body sensation and the second serves visual attention.
• That nucleus relays body sensation to the cortex.

• Localise the clue to the relevant anatomical level, cell type, pathway or molecular process.
• Map that structure or process to its normal function.
• Predict the deficit or clinical sign produced when it is disrupted.
• Reject options that belong to a neighbouring structure, pathway or level of explanation.