Figure 11. Proposed network architecture underlying thalamic α and θ rhythms.

The amplitude of thalamic α and θ rhythms is proposed to be determined by the destructive interference of competing, anti-phase groups of continuously bursting TC neurons which are sparsely connected by GJs. The salient aspects of this proposed scheme are as follows: i) HT bursting TC neurons (indicated in blue) are a subset of TC neurons comprising around ~25% of the total population and which are interspersed amongst conventional TC neurons (indicated in grey), ii) the majority of these HT bursting neurons are coupled by strong GJ connections (thick continuous lines) and form small, tightly correlated groups (e.g. neurons 2-5 and neurons 6-8), iii) such groups can be linked by a single weak GJ connection (i.e. thin dotted line between neurons 5 and 6) causing the bursting of these two groups to be consistently anti-phase to each other (Sherman and Rinzel, 1992; Sherman, 1994; Schweighofer et al., 1999; Bem and Rinzel, 2004), iv) at other points in the network, however, these groups can be linked by strong GJ connections (i.e between neurons 2 and 1 and subsequent cells, and between 8 and 9 and subsequent cells) which act as network ‘pivot points’ and which can facilitate the dynamic phase switching of large groups of neurons. These connections are proposed to occur between dynamically heterogeneous cells as indicated by the different shapes (see text). The overall result of this architecture is that there is a constant swapping of neurons between two populations which essentially burst in an anti-phase relationship to each other with this being dynamically reflected in the amplitude of the field oscillation (see the vertical dotted lines and the way in which the depicted field oscillation is dependent on the proportion of neurons which fire in and out of phase at any one time). The green and red boxes highlight occasions where pairs of TC neurons undergo a phase reset or a ‘drifting out of phase’, respectively (cf. Figs. 9A₃ and 10C).