Thalamo-cortical interactions modeled by forced weakly connected oscillatory networks

In this paper we do not discuss what a thalamo-cortical system modeled by a weakly connected oscillators can do, but we rather discuss what it cannot do. Interactions between any two cortical columns having oscillatory dynamics crucially depend on their frequencies. When the frequencies are different, the interactions are functionally insignificant (i.e., they average to zero) even when there are synaptic connections between the cortical columns. We say that there is a frequency gap that prevents interactions. When the frequencies are equal (or close) the oscillators interact via phase deviations. By adjusting the frequency of oscillations, each cortical column can turn on or off its connections with other columns. This mechanism resembles that of selective tuning in frequency modulated (FM) radios. A weak non-constant thalamic input can remove the frequency gap and link any two oscillators provided the input is chosen appropriately. In the case of many cortical columns with incommensurable frequency gaps the thalamic forcing will be chaotic. By adjusting its temporal activity, the thalamus has complete control over information processing taking place in important parts of the cortex