The thalamus is located in the diencephalon, which consists of the epithalamus, the thalamus, the subthalamus and the hypothalamus. The diencephalon is situated between the cerebral hemispheres and the brain stem. The thalamus is the largest part of the diencephalon. The thalamus has multiple functions. It plays an important role in sensory and motor functions, as well as pain and emotion.
The thalamus consists of numerous nuclei, which have connections between the peripheral nervous system, the brain stem and the cerebral hemispheres. Some nuclei receive input from cortical structures in the brain and relay the information to the body, while other nuclei receive information from the body and relay the information to the brain. The thalamus consists of two halves, the right side and the left side. The right nucleus receives inputs from the left side of the body and vice versa.
The ventroposterolateral nuclei are involved in sensation from the contralateral side of the body. The ventroposteromedial nuclei are involved in taste sensation and sensation from the contralateral face. The medial geniculate nuclei are involved in hearing, while the lateral geniculate nuclei and the pulvinar are involved in vision. Therefore a stroke affecting the thalamus may result in loss of sensation from the face or body, and may also affect hearing and vision. The thalamus does not play a role in the sensation of smell.
The execution of a simple movement such as taking a glass of water and drinking from it is a complicated task in the brain that involves numerous neurons, coordinating different parts of the brain and different muscles. Much of the coordination is the job of the thalamus. The ventrolateral nuclei and the ventrointermedial nuclei are responsible for coordination of movement. The ventroanterior nuclei are responsible for planning and initiation of movement. Thalamic stimulation or thalamic surgery have been used to try to alleviate motor disorders such as Parkinson’s disease.
The anterior nuclei are involved in memory and emotion. This is why memory always evokes emotion, because both are controlled by the same neuronal pathways in the brain at the thalamus. Emotion can also be a great motivator. The mediodorsal nuclei are involved in motivation and drive. The centromedian nuclei are involved in pain and emotion. Strokes affecting the thalamus can cause mood swings and also neuropathic pain.
The thalamus also plays a part in regulating sleep and wakefulness. As it receives sensory signals from the body, including touch and sounds, it can shut down these signals, preventing them from waking one up from sleep.