The involuntary nature of conversion disorder, 2010, V. Voon et al.

The involuntary nature of conversion disorder
V. Voon, C. Gallea, N. Hattori, MD, M. Bruno, V. Ekanayake, M. Hallett

BACKGROUND
What makes a movement feel voluntary, and what might make it feel involuntary? Motor conversion disorders are characterized by movement symptoms without a neurologic cause. Conversion movements use normal voluntary motor pathways, but the symptoms are paradoxically experienced as involuntary, or lacking in self-agency. Self-agency is the experience that one is the cause of one’s own actions. The matched comparison between the prediction of the action consequences (feed-forward signal) and actual sensory feedback is believed to give rise to self-agency and has been in part associated with the right inferior parietal cortex. Using fMRI, we assessed the correlates of self-agency during conversion tremor.

METHODS
We used a within-subject fMRI block design to compare brain activity during conversion tremor and during voluntary mimicked tremor in 8 patients.

RESULTS
The random effects group analysis showed that conversion tremor compared with voluntary tremor had right temporoparietal junction (TPJ) hypoactivity (p < 0.05 family-wise error whole brain corrected) and lower functional connectivity between the right TPJ, sensorimotor regions (sensorimotor cortices and cerebellar vermis), and limbic regions (ventral anterior cingulate and right ventral striatum).

CONCLUSIONS
The right TPJ has been implicated as a general comparator of internal predictions with actual events. We propose that the right TPJ hypoactivity and lower TPJ and sensorimotor cortex interactions may reflect the lack of an appropriate sensory prediction signal. The lack of a match for the proprioceptive feedback would lead to the perception that the conversion movement is not self-generated.

Link | PMC | PDF (Neurology)

 

Posting in relation to Walitt et al.

 

It then went on to say

Later on, it said same thing, only differently, regarding post-exercise MEP amplitude staying high:

It's as if they couldn't decide whether to attribute the performance difference to a brain dysfunction or conscious/unconscious pacing. Or, maybe the two are the same thing in their mind.

 

The argument in the conclusion of the 2010 paper looks bogus to me. Sense of agency and voluntariness are different things. If an apple rolls off the table I will involuntarily jump to catch it but am fully aware that it is 'me' jumping. On the other hand when I have vertigo I lose the automatic sense that my eye movements are mine, so the world seems to spin, but I can nevertheless try very hard to look in a direction.

In simple terms there is a difference between ' I wanted to do it' and 'it was me that did it'.

I very much doubt anyone knows enough detail about the function in these cortical areas to build meaningful theories of voluntariness.

It is not surprising that these tremors show different brain activity from deliberately created tremor. And anyone who has looked after such patients is aware that the tremor is not a normal deliberate action. Maybe it is good to know that this simple observation can be confirmed. However, the idea that you can use brain patterns to 'prove' theories about predictive coding or whatever seems very weak.

A glaring gap in conventional neuroscience accounts of predictive coding is the structural level at which the comparisons involved on conscious aspects of agency actually occur. I strongly suspect it is at a neuronal level and would not actually show up on imaging as such.

 

Thinking about this: I think I could argue that the time when we can interpret fMRI in terms of efforts, desires, agency or whatever will have come when the technology is good enough to provide legally robust reliable lie detectors.

As far as I know nobody is suggesting that we have that now. If we did there ought to be a law that anyone accused of a crime could take an fMRI lie test to prove their innocence!

 

I think the paper was suggesting that the lack of feed-forward prediction signal (due to rTPJ hypoactivity or such) is messing up the comparator, leading to the lack of the sense of agency. In mechanical terms, I can see the absence of feed-forward signal in the presence of the feed-back could lead to the missing sense of agency. It's like a light turning on by itself with nobody flipping the switch. Involuntary action would be more analogous to the light turning on automatically (with motion sensor, etc) rather than missing actuation. Whether the model/analogy/data are correct would be another question, of course.