A functional magnetic resonance imaging study of cortical asymmetry in bipolar disorder.
OBJECTIVE
Individuals with bipolar disorder (BPD) exhibit motor, perceptual, and cognitive disturbances involving predominantly right hemisphere dysfunction. This asymmetry has been used to advance the hypothesis that the pathogenesis of bipolar disorder may be related to disturbances of the right cerebral hemisphere. We employed functional magnetic resonance imaging to examine hemispheric asymmetries in manic and depressed BPD. A secondary goal of the study was to examine effects of psychotropic medications on blood volume changes in the motor cortices.


METHODS
We studied 18 right-handed BPD and 13 right-handed normal healthy comparison subjects. Blood oxygen level dependent (BOLD) responses in the primary motor area (M1) and supplementary motor area (SMA) of both hemispheres were elicited during reaction time (RT) tasks.


RESULTS
Healthy subjects activated the SMA in a reciprocal fashion with significantly greater activity in the left SMA for right hand trials and the right SMA for left hand trials. Depressed BPD subjects failed to show this normal reciprocity indicating a failure to suppress unwanted activity in the ipsilateral right SMA, whereas manic BPD subjects failed to suppress unwanted ipsilateral SMA activity in both hemispheres. Manic and depressed BPD subjects exhibited greater activity in the left primary motor area suggesting increased cortical excitability. BPD subjects treated with antipsychotics or mood-stabilizing medications exhibited longer RTs, lower BOLD responses in M1 and SMA, and a loss of normal hemispheric asymmetry in the SMA than untreated subjects.


CONCLUSIONS
The presence of a right hemisphere disturbance in BPD is consistent with the hypothesis that the right hemisphere may be dominant in mood regulation. The presence of both left and right hemisphere disturbances in mania may explain the coexisting psychotic and affective symptoms observed in this condition.
Caligiuri
Michael P
MP
Department of Psychiatry, University of California at San Diego, and VISN-22 Mental Illness Research, Education, and Clinical Center, VA San Diego Healthcare System, USA. mcaliguiuri@ucsd.edu
Brown
Gregory G
GG
Meloy
M J
MJ
Eyler
Lisa T
LT
Kindermann
Sandra S
SS
Eberson
Sonja
S
Frank
Lawrence R
LR
Lohr
James B
JB
D000328:Adult; D001714:Bipolar Disorder / Q000175:diagnosis / Q000378:metabolism* / Q000628:therapy; D001921:Brain / Q000378:metabolism*; D039721:Diagnostic and Statistical Manual of Mental Disorders; D004565:Electroconvulsive Therapy / Q000295:instrumentation; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009044:Motor Cortex / Q000378:metabolism; D011930:Reaction Time