Functional Magnetic Resonance Imaging of mental rotation and memory scanning: a multidimensional scaling analysis of brain activation patterns
permalinkBrain Research Reviews - 1998-01-01Tagaris GA, Richter W, Kim SG, Pellizzer G, Andersen P, Ugurbil K, Georgopoulos APMental rotation and memory scanning are typical examples of cognitive operations presumably involved in various tasks. The original tasks involved judgements to be indicated by key presses or verbal responses, whereas recent variants required directed movements as responses. The cardinal sign of both mental rotation and memory scanning tasks is the increase of the response time with task demands, namely the angle of rotation or of the number of items in the list scanned. The rates of processing information in these two kinds of tasks are uncorrelated, which suggests that different brain mechanisms may be involved. In contrast, the rates of rotation of a figure or a movement direction are positively correlated, which suggests that common aspects of brain mechanisms may be involved in widely different cases of mental rotation. The overall brain mechanisms underlying mental rotation and memory scanning are largely unknown. With respect to mental rotation, a consistent finding of electrophysiological and other studies has been that parietal areas are involved in mental rotation of visual images. With respect to relations between brain activation and task performance, recent studies using
Functional Magnetic Resonance Imaginghave indicated an involvement of the parietal areas, bilaterally, with performance outcome and an association of the precentral gyrus of the right hemisphere with the rate of mental rotation in the Shepard and Metzler image paradigm. Neurophysiological studies in the motor cortex of behaving monkeys have provided an insight into the neural processes involved in the mental rotation and memory scanning tasks that required directed movements as indicators of response; namely, a slow rotation of a directional population signal in mental rotation and an abrupt switch in direction of that signal in memory scanning. Although these studies addressed the question of neural processing within a particular cortical area (i.e. the motor cortex., several brain areas are probably involved in the performance of these tasks. It is also obvious that tasks can resemble) or differ from. each other along different dimensions. For example, some tasks involve mental rotation whereas others involve memory scanning; and some involve mental operations on visual images whereas others involve operations on movement representations. The constellation of brain areas that are differentially involved in, and essentially represent, those dimensions can be revealed best by techniques that allow the determination of engagement of a number of areas by a given task. This information can be obtained accurately in single subjects by
fMRIwhich we employed in this study.Typically, several areas are activated during performance of a given task, and this set of areas frequently overlaps with the set of another task. This, in turn, implies that task-related information is processed in a distributed fashion by various areas. In the present study, we sought to recover this information from binary functional activation maps using weighted multidimensional scaling.