Synapse Imperatives are all new powers of the Hive Mind. WarCom did a discussion on it and of course we have leaks that show them all as well, lets check them out.
via WarCom
Tyranid armies have always been guided by powerful SYNAPSE creatures, living psychic relays for the Hive Mind’s control – but these vital beasties are now packing a set of all-new powers known as Synaptic Imperatives.If every unit from your army has the HIVE TENDRIL keyword, and they all come from the same Hive Fleet,* then at the start of each battle round you can choose to activate one Synaptic Imperative. These are powerful, aura-like abilities that radiate from each and every SYNAPSE unit in your army until the end of that round – and depending on your swarm’s composition, you’ll be able to pick between a jaw-dropping 10 of them.Each breed of SYNAPSE creature in your army grants access to a different Synaptic Imperative – think of it as a beast transmitting its specialised instincts across the rest of the Hive Mind’s command beacons. So if you have a Hive Tyrant in your army (perhaps courtesy of the massive new Combat Patrol), you’ll be able to activate the Relentless Ferocity ability.
Here is what the leaks reveal as found on Reddit
