Injury to the thalamus and its connections related to cognitive deficits.

Reviewing Brain Scan

Approximately the size and shape of a big egg, the thalamus is located deep and somewhat center in the brain. Thick projections of white matter connect the thalamus to other areas of the brain, which is why the thalamus to often referred to as a "relay system" of the brain, or in simpler terms, "Grand Central Station."

Therefore, when the thalamus or its many connections are damaged through direct injury or diffuse axonal injury (where the white matter tracts are stretched or severed), it may be concluded that the connected areas of the brain are also affected. In other words, if Grand Central Station is down, so are its incoming and outgoing destinations. Damage to the thalamus or its connections can result in widespread functional impairment.

The frontal lobe is heavily connected to the thalamus. It is also associated with cognitive abilities such as memory or executive functioning. In cases of traumatic brain injury, however, the relationship between damage to the white matter connections from the frontal lobe and cognitive impairment has generally been weak.

Medical researchers from Chicago recently hypothesized that damage to these incoming and outgoing connections could lead to cognitive impairment. They used diffusion tensor imaging to verify that lesions in projections into the thalamus were indeed significantly associated with cognitive impairment-the greater the lesions, the greater the impairment. This research provides further support that cognitive impairment related to the frontal lobe need not have originated from direct frontal lobe damage.

Little DM, Kraus MF, Joseph J, et al. Thalamic integrity underlies executive dysfunction in traumatic brain injury. Neurology. (February 2010).