I also have treatment resistant depression. I've become ever more emotionally numb, my memory and focus has been deteriorating for some time now. My pdoc has recommended TMS for awhile, several months, years maybe - I've been depressed for so long, and the constant stress. I finally agreed but my insurance will make me jump through hoops.

I'd suggest reducing the stress in your life, engaging socially, reading non-fiction that is somewhat demanding of your attention, exercising, multi vitamin/mineral supplement (I recommend Twinlab dual tabs), fish oil supplement, abstaining from refined sugars/processed foods, a diet of whole foods (brown rice, quinoa, oatmeal, beans, lintils, vegatables, fresh fruit, nuts, honey, seeds, spinach, coconut oil, ginger, egg whites, chicken, some steak, etc), and seeing if you can get TMS treatment.

I've been seeing some improvements from diet, exercise, and reading. I know I should get back to relearning algebra, it really helped improve working memory, but the motivation I had to do so is no longer present. I was preparing for another semester of college, it was a tiring effort, but I could not attend because I was, and still am, unable to secure transport. Sigh..tried so hard, struggled with the algebra through fall, most of spring.. I guess I just want to convey that I may comprehend some of the stress you are probably experiencing.

The social aspect is personally daunting for me, but I have read enough abstracts on phys.org over the years to understand the more the brain is engaged in activities the more adept it can become in those activities. I should also see a CBT but, again, transportation issues.

Another possibility to consider, with skepticism and extensive reservations, is a supplement called Sensoril. Some studies indicate it might aid in improving certain aspects of cognition in individuals with bipolar such as auditory processing and working memory. I don't know if it works and probably won't be able to know for a great deal of time. Nearly all of the alternative treatments are pure snake oil though, so don't get fooled into believing any of the BS marketing. The only reason I even bothered considering Sensoril is that the plant extract it is derived from (ashwaganda/withania semnifera) has its origins in Indian medicine that has been in use for ages. Also, green tea has shown some promise in improving working memory in a short-term basis, not merely because of caffeine content. Get tea leaves, not bags.

That's about all I know on how to battle the cognitive decline severe depressive episodes of bipolar can have. I'm still trying to figure it out ><.