Modulation of effective connectivity by cognitive demand in phonological verbal fluency.
Verbal fluency is a classic neuropsychological measure of language production. Phonological verbal fluency involves the generation of words beginning with a specified letter, and its functional neuroanatomy is comprised of a distributed network of regions which is modulated by cognitive load. In order to investigate the functional relationship of these regions, the effective connectivity was analyzed with covariance structural equation modeling under conditions of varying cognitive load. Significant path coefficients were evident between the anterior cingulate, left middle frontal gyrus, and precuneus. The left middle frontal gyrus showed a facilitory projection to the precuneus which had a suppressive influence on anterior cingulate activation. With increasing cognitive demand, the left middle frontal projection to the precuneus became suppressive, and the path coefficient from the precuneus to the anterior cingulate showed a marked diminution in strength. The path analysis suggests that the lead-in process for letter verbal fluency may primarily involve an orthographic visual strategy. The marked changes in path coefficients with the increased cognitive load may reflect the greater demands placed on executive function. The significant changes in path coefficient values with increased cognitive demand indicate the importance of accounting for task difficulty not only in the interpretation of brain activation maps but also for effective connectivity measurements.
Fu
Cynthia H Y
CH
Institute of Psychiatry, King's College London, 103 Denmark Hill, London, SE5 8AF, UK. c.fu@iop.kcl.ac.uk
McIntosh
Anthony R
AR
Kim
Jieun
J
Chau
Wilkin
W
Bullmore
Edward T
ET
Williams
Steve C R
SC
Honey
Garry D
GD
McGuire
Philip K
PK
D000328:Adult; D001288:Attention / Q000502:physiology; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D004292:Dominance, Cerebral / Q000502:physiology*; D005625:Frontal Lobe / Q000502:physiology; D006179:Gyrus Cinguli / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D015233:Models, Statistical; D009415:Nerve Net / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology; D010700:Phonetics; D013068:Speech Production Measurement; D014705:Verbal Behavior / Q000502:physiology*