Knowable magazine, which covers research published in Annual Reviews journals, has a nice interview by writer Emily Underwod of Michael Halassa, an expert on the functional neuroscience of the thalamus: “A long-overlooked brain region may be key to complex thought”.
In the interview, Halassa emphasizes that the thalamus has often been assumed to function basically as a relay station between the senses and the cortex, based mainly on visual processing as a model for the rest:
What’s so interesting about primate vision and visual cognition is that when we interact with the world, we’re not just interacting with pixel intensities, we’re building internal representations of objects. That’s why you can categorize any cup you see, even if you've never actually seen that particular cup before, and it looks different from other cups. Neurons that can specifically recognize male or female faces, or respond only to a photo of Jennifer Aniston — all that exciting stuff happens in the cortex, which is part of the reason that the thalamus has been sort of shoved to the side.
But there are many other areas of the thalamus besides the LGN and other sensory areas that interact with the cortex, including areas involved in motor control and cognition. Now we are studying those too.
If you did purely imagine the thalamus as a relay station, that would not mean it was unlikely to be important to cognition. In the real-world telecommunications network, relays have to work fast and flawlessly. But to evolution, noise in a relay system is potentially a source of adaptive variation. A small change to the relay, like a slightly greater or lesser degree of crosstalk to one or another region, might often be a negative, but once in a great while might have an effect on cognition that enhanced survival or reproductive fitness. Even if the relay functions are strongly conserved among species, getting these connections slightly wrong would occasionally be useful in one or another lineage.
Humans, with a rapidly evolving brain and vastly larger cortex, might be just the lineage in which “wrong” connections might have a positive effect once in a while.