Neural dynamics in Parkinsonian brain: The boundary between synchronized and nonsynchronized dynamics

Synchronous oscillatory dynamics is frequently observed in the human brain. We analyze the fine temporal structure of phase-locking in a realistic network model and match it with the experimental data from Parkinsonian patients. We show that the experimentally observed intermittent synchrony can be generated just by moderately increased coupling strength in the basal ganglia circuits due to the lack of dopamine. Comparison of the experimental and modeling data suggest that brain activity in Parkinson's disease resides in the large boundary region between synchronized and nonsynchronized dynamics. Being on the edge of synchrony may allow for easy formation of transient neuronal assemblies.

Figure 1

Model network. Arrows indicate connections between cells (solid, excitatory; dashed, inhibitory).

Figure 2

First-return maps. (a) The diagram of the map. The phase space is partitioned into four regions; arrows indicate all possible transitions between them, and transition rates are written next to the arrows. (b),(c) Examples of the maps derived from experimental and model data, respectively. Four maps in (b) and (c) have the same data points; lines illustrates the transitions from points in different regions.

Figure 3

Experimental and modeling transition rates (a) and duration of desynchronization events (b). Stars represent modeling rates; gray bars and standard deviations are for the experiment. Duration is measured in the number of cycles of oscillations. The distributions are similar and share the same features (dominance of short desynchronization events). Parameter values are the same as in Fig. 2c; experimental rates are from [15].

Figure 4

The model dynamics in dependence on $g_{\mathrm{syn}}$ and $I_{\mathrm{app}}$ vs experimental data. The circles indicate the number of principle components capturing 80% of variation in the principle component analysis for the slow variables $r$ of all STN cells in the model. The lines represent the contours of the parameter domains, where the model rates $r_i$ characterizing the temporal structure of synchronization are within 0.7 SD of the experimental rates. Solid, dotted, and dashed lines correspond to different values of the weights used to compute model LFP (0.26, 0.3, and 0.35).