A growing body of evidence suggests that the thalamus – that walnut-shaped chamber buried deep within the brain – regulates our thoughts, perceptions, and behavior far more than most scientists believed.
As discussed in the latest issue of the journal Neuron, studies are showing that the thalamus sometimes controls the focus of our visual attention more than the visual cortex does, and that it may act as an attention “gatekeeper,” holding our focus where it thinks is most important.
The thalamus also seems to play an active role in determining what visual information we get to consciously perceive, and it even has some control over the firing of neurons in cortical areas associated with planning and movement – which means the thalamus may not only be telling us what we see, but also what we think, and how we’re going to act.
But before anyone starts writing angsty punk-rock songs about the thalamus, I should point out that the cerebrum – the cauliflowery part of the brain that allows us to be conscious – also seems to have a major influence on thalamic activity – which means the thalamus may be sensitive enough to base its routing and gatekeeping decisions on what we’re thinking and feeling at the time:
The overall evidence that has emerged during recent years suggests that the visual thalamus serves a fundamental function in regulating information transmission to the cortex and between cortical areas according to behavioral context.
If this all sounds confusing, that’s because it is – in fact, a lot of this data is so new and complex that even neuroscientists aren’t quite sure what to make of it.
Let’s back up a little and put this stuff in context. See, throughout most of the 20th century, most scientists thought the thalamus – named after the Greek word for “room” or “chamber” – was basically the brain’s mailroom – a passive relay station that routed sensory data to and from various parts of the cerebrum (presumably in between hour-long smoke breaks).
But in the ’80s, evidence began to emerge that the thalamus had a much more complex job description – for example, scientists discovered that some neural connections within the thalamus could influence others, suggesting that the thalamus took a highly active role in deciding which signals were passed on, and where they went.
And yet, for various reasons, a lot of these exciting discoveries didn’t generate much follow-up for the next 20 years or so. Instead, neuroscientists told the thalamus they were “just feeling confused” about their relationship with it, and that they needed to “take some time to see other brain structures.”
And so, those scientists turned their new imaging technologies, like fMRI, on the cerebrum, mapping its activity with ever-greater precision. But by the early ’00s, many neuroscientists had decided they missed the thalamus, and they spent night after night desperately holding up a boombox outside its window.
Nowadays, the thalamus is finding itself back in the spotlight, as scientists have discovered more and more of its amazing abilities. For example, subjects with lesions to the little-studied pulvinar region of the thalamus experience some bizarre symptoms, such as mistaking the color of one object for the color of one close by, trying to grasp an object by grasping nearby empty air, and having serious trouble directing their attention to a specific spot.
Aside from being (in scientific terms) “hilarious,” these symptoms also tell us that the pulvinar thalamus is necessary for all sorts of basic visual tasks. This has led some scientists to propose that the modulatory action of the thalamus helps synchronize signals from various cortical areas – and some of the latest research seems to back this up.
Though a lot of this research has been focused on the visual pathway, it seems reasonable that similar rules hold for the rest of our sensory experience:
The visual thalamus serves as a useful model for the thalamus in general because of common cellular mechanisms and thalamo-cortical connectivity principles across different sensorimotor domains.
Still, not many scientists have studied the way the thalamus acts in “awake, behaving” animals – so it’s going to take a lot more research before anyone fully understands exactly what role of the thalamus plays in our perception and cognition.
So for now, it’s probably best to play it safe, and not say or write anything insulting about this weird and suspicious-sounding part of the brain; otherwise it may snap and decide to
ALL HAIL THE MIGHTY THALAMUS! THALAMUS IS THE GREATEST AND MOST AWESOME BRAIN REGION! ALL OTHERS ARE PATHETIC!