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Archive for 02/12/2010

Super MRI

One of the reasons that the neo-cortex has center stage in our view of the brain is that it is big, very big; another is that it is relatively bigger in humans than in animals; and finally is the fact that we can examine it more easily than other parts of the brain. So, hey, it just must be the center of thought. A trick to correct this habit of thought for a few moments now and then is to envision the neo-cortex as the computer used by the thalamus, archeocortex and basal ganglia to do the donkey work in sorting out the detail in perception, motor programming etc. You may not want to get too fond of this picture but it is a good antidote for the continuous emphasis of the neo-cortex.

Things may change. It seems that a more powerful fMRI is now available and it can actually show specific parts the the thalamus etc. ‘lighting up’. Here is the abstract of a recent paper from Otto-von-Guericke University:

Thalamocortical loops, connecting functionally segregated, higher order cortical regions, and basal ganglia, have been proposed not only for well described motor and sensory regions, but also for limbic and prefrontal areas relevant for affective and cognitive processes. These functions are, however, more specific to humans, rendering most invasive neuroanatomical approaches impossible and interspecies translations difficult. In contrast, non-invasive imaging of functional neuroanatomy using fMRI allows for the development of elaborate task paradigms capable of testing the specific functionalities proposed for these circuits. Until recently, spatial resolution largely limited the anatomical definition of functional clusters at the level of distinct thalamic nuclei. Since their anatomical distinction seems crucial not only for the segregation of cognitive and limbic loops but also for the detection of their functional interaction during cognitive-emotional integration, we applied high resolution fMRI on 7 Tesla. Using an event-related design, we could isolate thalamic effects for preceding attention as well as experience of erotic stimuli. We could demonstrate specific thalamic effects of general emotional arousal in mediodorsal nucleus and effects specific to preceding attention and expectancy in intralaminar centromedian/parafascicular complex. These thalamic effects were paralleled by specific coactivations in the head of caudate nucleus as well as segregated portions of rostral or caudal cingulate cortex and anterior insula supporting distinct thalamo-striato-cortical loops. In addition to predescribed effects of sexual arousal in hypothalamus and ventral striatum, high resolution fMRI could extent this network to paraventricular thalamus encompassing laterodorsal and parataenial nuclei. We could lend evidence to segregated subcortical loops which integrate cognitive and emotional aspects of basic human behavior such as sexual processing.

All the anatomical detail aside (not that it is not important) what we are finally coming close to seeing is the heart of the system – the interaction of the various parts of the brain, the important feedback loops, and not just the neo-cortex. I believe that we need to understand those loops before we can come close to understanding the mind. We have a new window – great.
Metzger CD, Eckert U, Steiner J, Sartorius A, Buchmann JE, Stadler J, Tempelmann C, Speck O, Bogerts B, Abler B, & Walter M (2010). High field FMRI reveals thalamocortical integration of segregated cognitive and emotional processing in mediodorsal and intralaminar thalamic nuclei. Frontiers in neuroanatomy, 4 PMID: 21088699