How is memory loss related to depression?

It slows brain work. Major Depression is a neuropsychiatric illness; it involves changes in brain centers involved in the regulation of mood, enrgy, thoughts, judgement, planing, appetite, sleep, memory, and perception of self and others; These changes happen due to alteration in neurotransmiters, and receptor responcivity and other hormonal factors; When the depression is alleviated memory improves;
Two ways. When people are depressed sometimes their ability to concentrate is impaired resulting in troubles with memory. This type of memory problem should correct when the depression is treated. Also with some memory problems like Alzheimer's disease depression can also occur. In those patients treating the depression may not improve memory problems.