Estradiol, progesterone and pregnenolone synergistically improve cognitive function and a sense of calmness. 

I think we are learning a lot lately about how shutting down these hormones can affect us emotionally.

TRT shuts down or reduces upstream hormones like pregnenolone and progesterone.  The HPTA shut down of LH and FSH also has implications.  We need LH to activate  Steroidogenic acute regulatory protein (StAR) to make upstream hormones while on TRT. In the absence of LH, HCG can do the trick to wake up the production of pregnenolone and progesterone (taking pregnenolone supplements can also accomplish this but without StAR activation).

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LH activates the areas shown as stars. TRT shuts down LH and thus several hormones upstream of testosterone. HCG can mimic LH's effect and compensate for this shut down.

As time goes by, the use of TRT+HCG will grow stronger as more data is generated on this fact.

All steroid hormones are derived from cholesterol.  A series of enzymatic steps in the mitochondria and  endoplasmic reticulum (ER) membrane of steroidogenic tissues convert cholesterol into all of the other steroid hormones and intermediates.

The rate-limiting step in this process is the transport of free cholesterol from the cytoplasm into mitochondria.  This step is carried out by the Steroidogenic Acute Regulatory Protein (StAR)

Activating StAR has many benefits (read the link above).

Human chorionic gonadotropin (hCG) regulates the expression of Steroidogenic acute regulatory protein (StAR) via the ERK1/2 pathway