Instability and pattern formation in the human brain during complex sensorimotor and auditory tasks as revealed by magnetoencephalography

Following Kelso et al. (1991a; 1992), Wallenstein et al. (1995), Tuller et al. (1994), and Case et al. (1995); see also Fuchs et al. (1992), the experiments described in this research all used a dynamical methodology designed to produce a coherent brain state and then lead that brain state through a spontaneous reorganization via the influence of a parametric change. Magnetoencephalographic (MEG) recordings made during the spontaneous behavioral and perceptual transitions were analyzed by decomposition of the brain's high-dimensional magnetic field into a few task-relevant components. The analysis showed that the dynamics of the MEG signal, including the reorganization which occured as a result of the parametric manipulation, could be accounted for by the dynamics of the individual components. This supports the idea that the task requirements in each case placed the brain into a (relatively) low-dimensional state through the cooperative interactions among the many neuronal elements involved in the task. The experiments included two coordination experiments in which subjects were required to produce index finger flexions in time to an auditory metronome in an anti-phase pattern while the metronome rate was increased. Increases in the variability of both the behavior and the motor-associated magnetic field components prior to the transition to an in-phase pattern support the hypothesis that a dynamic instability mechanism exists for pattern formation and change during those tasks. In the third experiment a perceptual instability was explored by systematically scaling a parameter known to influence categorization of speech stimuli: biasing the transition created stimuli that were perceived in two different ways. The design of the experiment allowed the investigation of neural correlates of the physical properties of the stimuli, perceptual invariance, bistability, and perceptual reorganization. Analysis of the MEG signals suggests that presentation of a bistable stimulus places the brain into a highly sensitive, unstable state that can be influenced by ongoing activity.