To the Editor:

I read with great interest the recent article by Liu et al.1  regarding neural basis of consciousness. However, as a neurologist with interest in laterality of motor control and consciousness,2–5  I would like to add the following perspective for further understanding the problem that they have studied.

Contrary to the assumption of the authors, as delineated in the above-mentioned references, consciousness exclusively lies in the major hemisphere (i.e., hemisphere of speech and action) with the minor hemisphere (i.e., the right in 85% of the population) tasked with functioning at the behest of the major hemisphere for events occurring on the nondominant side of the body/space. It has also been shown that handedness is a fairly authentic representation of the hemisphere housing consciousness, with the nondominant side being farther away from the command center by an interhemispheric transfer time. Sensory-wise, too, stimulations of the nondominant side of the body arrive at the conscious hemisphere at a delay that amounts to an interhemispheric transfer time. All these occur because of the fact that signal traffic within the corpus callosum is one-way; from the major to the minor hemisphere for the somato-motor events and in the opposite direction for the somato-sensory ones. Unfortunately, in the article in question the authors neither refer to the handedness of their participants, nor did they indicate the laterality of the commands to be carried out by their subjects (squeezing the hand of the examiner or taking a deep breath, page 60).

Nevertheless, because in “using functional magnetic resonance imaging, the authors demonstrated that propofol conferred differential changes in functional connectivity of the specific and nonspecific thalamocortical systems, particularly in left hemisphere,” one may conclude that the subjects were indeed right handed. However, ascribing the latter finding to the verbal nature of stimuli and tasks is not justified because the same finding would have been expected if the subjected pantomimed or imagined the same activities.6 

References

1.
Liu
X
,
Lauer
KK
,
Ward
BD
,
Li
SJ
,
Hudetz
AG
:
Differential effects of deep sedation with propofol on the specific and nonspecific thalamocortical systems: A functional magnetic resonance imaging study.
Anesthesiology
2013
;
118
:
59
9
2.
Derakhshan
I
:
Voluntary brain processing in disorders of consciousness.
Neurology
2009
;
73
:
1712
author reply 1712–3
3.
Derakhshan
I
:
Nonconvulsive status epilepticus with an unusual EEG: A fresh look at lateralities of motor control and awareness.
Epilepsy Behav
2006
;
9
:
204
10
4.
Derakhshan
I
:
Bimanual simultaneous movements and hemispheric dominance: Timing of events reveals hard-wired circuitry for action, speech, and imagination.
Psychol Res Behav Manag
2008
;
1
:
1
9
5.
Derakhshan
I
:
Laterality of motor control revisited: Directionality of callosal traffic and its rehabilitative implications.
Top Stroke Rehabil
2005
;
12
:
76
2
6.
Moll
J
,
de Oliveira-Souza
R
,
Passman
LJ
,
Cunha
FC
,
Souza-Lima
F
,
Andreiuolo
PA
:
Functional MRI correlates of real and imagined tool-use pantomimes.
Neurology
2000
;
54
:
1331
6