Never been to Briarwood specifically but I've done a fair bit of work in decommissioned psychiatric facilities over the years - Severalls in Essex, High Royds up in Yorkshire. The energy in those places is unlike anything else.
What you tend to find with sanitariums is layered activity - you've got residual haunting from decades of sustained emotional trauma, but also what I'd classify as intelligent responses. Different beast entirely.
A few questions worth asking if you're investigating there:
What ward sections are most active? Admin buildings tend to be quieter than the treatment wings, Any reports of shadow figures or just auditory phenomena?, Has anyone attempted full-spectrum photography? I run a Sony A7 converted full-spectrum and the results in similar locations have been genuinely difficult to explain away
The demonological angle interests me with these sites too. Prolonged suffering in an enclosed space over generations can attract things that feed on residual trauma. Not saying that's what you've got, but worth ruling out.
Would love to see any EVP recordings or photographs if you've captured something. Post them up - this community is pretty good at picking apart the genuine from the pareidolia.
What's the history of the place specifically? When did it close, and were there any particular incidents on record?