This paper presents a 32-channel brain-computer interface SoC for closed-loop deep-brain stimulation in psychiatric disorders. The SoC integrates a 32-channel analog front-end, an efficient logarithmic feature extraction engine, a neural additive model classifier with online update, and a multimode stimulation controller. Fabricated in 65nm CMOS, the 5.46mm² SoC consumes 6.14µW/channel, enabling accurate, low-power, and adaptive detection of psychiatric states.