u/JooAssaasin

So both the Limbic system and Reptilian brain are both voiced by Mikee Goodman and both are heard when Harry sings at the Whirling in Rags. Both voices are heard during Karaoke depending on your skill check.

But the Limbic system is only heard during a failed check which is the key factor here. Harry is straining his voice trying to hit high notes out of his vocal range whereas during a successful check he keeps it within his range and avoids singing altogether hence why this is seen as a successful check.

Meaning both are the voices of Harry but the Reptilian brain is mostly likely how he sounds in normal conversation there wouldn't be a reason for him to put on a deep voice in a spoken word performance.