Finally, based on the above findings, we formalized a theoretical ‘bandwidth model’ of FOG to organically explain these observations (Fig. 7). The ‘bandwidth’ mimics the processing resource in human brains. The model consists of three main elements, (i) the baseline occupation; (ii) the dynamic fluctuation; and (iii) the bandwidth limit. The ‘baseline occupation’ depicts the occupation of cortical processing resources by the elevated neuronal synchrony, which can be quantified through M1 PAC and reflects the degree of motor impairment under a certain condition. The ‘dynamic fluctuation’ reflects the instantaneous cognitive burden, which changes dynamically with time. And the ‘bandwidth limit’ defines a threshold when it is exceeded, information processing overloads and freezing occurs. The blank zone laid between the bandwidth limit and baseline occupation is the ‘available bandwidth,’ whose area represents the instant available neural processing resource. STN-DBS exerts therapeutic effects on FOG by both reducing the baseline occupation and elevating the bandwidth limit.
