So I was reading a paper that correlated thalamus activation during an fMRI cognitive control task to clinical outcomes. I'm wondering what it really means. I see thalamus all the time in my reward work, and considering how the thalamus is supposedly the sensory-input relay to cortex, and how it has all these other cortical loops, I typically chalk up thalamus activation to a somewhat non-specific epiphenomenon, like arousal. Indeed, when I go to neurosynth.org and its reverse-inference tab and put the cross-hairs in the thalamus, a whole HOST of cognitive functions activate it with high probability. I'm just wondering if there are any good papers out there that integrate fMRI papers (and maybe other data modalities) in service of unpacking what the thalamus does and when it IS vs ISN'T engaged by certain task demands. Any ideas? It would be great if this correlation had a true mechanistically-plausible underpinning.
Hi, I am also interested in individual difference in thalamus, but I more focused on the pulvinar nucleus of the thalamus. The pulvinar complex is the largest nuclear mass in the primate thalamus. Neuroimaging and lesion studies suggest that pulvinar is involved in attention and/or distractor filtering. Recently, Pesssoa and Adoplhs (Pessoa, L. and R. Adolphs (2010). "Emotion processing and the amygdala: from a 'low road' to 'many roads' of evaluating biological significance." Nat Rev Neurosci 11(11): 773-783.) suggest that pulvinar may play a part in evaluation of the biological significance of affective visual stimuli. As your mention that you see thalamus all the time in your "reword" work, I think this may be relevant.
http://www.ncbi.nlm.nih.gov/pubmed/20959860
Dear James Bjork,
this is indeed a very interesting question. From my point of view one has to separate the answer into two distinct parts: Which "activation" reflects task-specific and sensory demands and which activation is asociated with more unspecific effects such as vigilance alterations during the task.
During an simultaneous EEG-fMRI measurement
(http://www.ncbi.nlm.nih.gov/pubmed/19110062)
we found that thalamic BOLD signals decreased during lower (EEG-derived) vigilance stages in comprison to high vigilance stages while cortical activity showed the opposite pattern.The thalamus as the "gate of perception" seems to decrease its activity (by means of BOLD-activation) during low arousal levels. This may be interpreted as a "switch-off" during decline from wakefulness toward drowsiness so no more information gets through to the cortex. However, the cortex itself showed a high BOLS signal.
One might hypothesize that the thalamus BOLD activity reflects 1) the "flow-rate" of sensory input to the cortex (high BOLD signal = high flow) and 2) the degree of cortical "dissociation" from the external world by means of arousal and vigilance (low BOLD signal = low vigilance).
Sebastian
There may be several reasons responsible for individual differences in fMRI task signals. As our knowledge is improving about the network basis of a functional brain there might be several input and output from thalamus contributing to the individual differences in BOLD signals. At network level thalamus receive and send signals from the cortical and sub-cortical areas and everyone's brain functional connectivity to these different sub-networks of thalamus might be more or less activated during the task and may be affecting the BOLD signals. There are inherent differences in individuals brain (may due to genetic differences, environmental or social-environmental interactions) which can also be a major contributing factor in differences even if you are just looking at the task related BOLD signals thalamus. One the way to look at this is activation and deactivation of the thalmo-cortical network and look at differences in the ratio of BOLD signal in both condition.
ks
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