Alexandros Gelastopoulos Beta1 rhythm in parietal cortex can facilitate memory and modulate the ability to drive downstream targets. Alexandros Gelastopoulos Nancy Kopell's lab Boston University Brown University May 25th 2017

Overview Beta1 in the parietal cortex Driving a beta1 network with gamma Relation to speech processing

Gamma/beta2 to beta1 (15 Hz) Switches Roopun et al 2006, 2008 In vitro (S2, rodent) With kainate: gamma superficially, beta2 in deep layers Lower kainate: beta1 in both deep and superficial layers Separating layers destroys the beta1 rhythm everywhere Switch to beta1 only seen in parietal cortex superficial deep

I Gamma and beta2 mechanisms E Gamma (30-100Hz) can be generated by a population of excitatory and inhibitory interneurons (Pyramidal-Interneuronal Gamma – PING rhythm). In parietal cortex, deep layer pyramidal cells (intrinsically bursting – IB) can generate beta (~25Hz) by themselves. Not dependent on synapses. Beta in sensory cortex is synaptic. E I Kramer, et al 2008 Roopun et al 2010

Beta1 in parietal cortex: Mechanism Kramer, Kopell, Roopun, Whittington… 2008 Model reproduces behavior for both beta2+gamma and beta1 Gamma and beta2 periods concatenate to produce beta1 Concatenation created by inhibitory rebound Experiments validate model Plasticity among IB cells allows the rhythm to continue after initial stimulus has faded.

Simplified model of beta1 Simplified version of the network producing beta1 Behavior in the absence of inputs RS FS SI IB

Beta1 continues even if superficial layers are driven by gamma RS cells are entrained to gamma Beta1 continues RS cells and IB cells fire out of phase SI and IB periods concatenate to get beta1 SI cells participate in two rhythms

X X X Equality of SI and IB firing rate SI and IB cells have equal firing rates, even if the IB->SI and all synapses onto IB cell are removed IB can determine the SI firing rate, by indirectly inhibiting it IB->SI and SI->IB synapses facilitate the firing rate equality

Beta1 continues even if superficial layers are driven by gamma RS cells are entrained to gamma Beta1 continues RS cells and IB cells fire out of phase SI and IB periods concatenate to get beta1 SI cells participate in two rhythms

Silencing SI cells makes deep layers synchronize with input With gamma input Without input RS and IB cells fire in phase Synchronous deep-superficial layer activity might allow activation of downstream targets from common activity. VIP cells inhibit SOM+ SI cells. They are active during „hypervigilance”.

Stronger gamma input turns off SI cells by activating FS cells earlier Weak input Strong input Stronger input activates FS cells directly Submillisecond change in FS timing can inhibit SI cells

Cell assemblies can form with gamma input Gamma cell assemblies can form in response to phasic input Old input is remembered

Bastiaansen, Magyari, Hagoort 2009 Beta1 in speech processing Bastiaansen, Magyari, Hagoort 2009 Linear increase in beta1 power over time for syntactically correct sentences No beta1 power for randomized word order Beta1 power abolished when a word category violation occurs Effect seen in midfrontal and parietal areas

Integration of New Word into Cell Assembly Previously activated column targets columns associated with possible new words. Beta 1 from old column entrains new col to beta1. Sup. layers of new col. do not manifest beta 1 (before input) Activation of that column by correct word leads to full beta1, coordinated with previous cols. Beta 1 Not yet activated Beta 1 power builds up

Syntactically Wrong Word Yields Loss of Beta1 Beta 1 depends on timing of recurrent inhibition In absence of input, each layer is silent Bout of inhibition to deep layers can stop all activity Origin (?) of such inhibition: neurogliaform cells in “wrong col.” Lack of “preparation” to new col allows novelty response that activates NG cells Unprepared col reacts strongly to input.

Conclusions Previous work suggests that beta1 can support memory. - Special to parietal cortex Beta1 during speech is associated with syntactic processing Beta1 persists in the presence of superficial gamma input. - Old input can remain with new input and be kept separate. Turning on/off SI cells allows switching between synchronized/out of phase state. - Removal of SI cells can allow driving downstream targets. Beta1 power can build up linearly or be turned off, depending on whether a prepared/non-prepared column receives input.