Forming a memory of people, places, and events is a dynamic process, and many studies have shown that psychiatric disorders such as depression may affect this process.
Now researchers from the National Centre for Biological Sciences (NCBS), Bengaluru, have shown how memories change and get updated over time in people with unipolar and bipolar depression.
The study published in Neurobiology of Learning and Memory involved controls, unipolar- and bipolar-depression patients admitted at the National Institute of Mental Health and Neuro-Sciences (NIMHANS). Unipolar patients experience depressive symptoms such as low mood, lack of motivation, etc. whereas bipolar patients alternate between periods of depression and mania. Only bipolar patients in a depressive phase were included in the study.
Memory test
On the first day, all the participants memorised a list of 20 everyday objects. Two days later, controls, unipolar and bipolar patients were split into two groups, and the first group was prompted to remember what happened on the first day while the other group did not get this reminder. All the participants were then made to memorise a different list of everyday objects.
On the fifth day, all participants were asked to recollect the objects from the list shown on the first day.
Unipolar and bipolar patients remembered fewer objects than controls. The controls who were reminded recalled objects from the second list in addition to the first list. Such recall is a form of memory updation where new learning updates older memories, but only when the old memory is activated by a reminder. Controls who were not reminded did not recall objects from the second list.
In unipolar patients, this ability to update memories with a reminder was not affected and was similar to controls.
However, bipolar patients appeared to be mixing the objects from two lists during recall, irrespective of the reminder manipulation. “Though we asked only for objects from the first list, they also named items from the second list. Basically, they remembered the objects but had difficulty in remembering which list the object belonged to – a phenomenon known as source confusion in psychology. This mixing was not seen in unipolar or the control group,” explains Bhaktee Dongaonkar, a postdoctoral fellow at NCBS and first author of the paper.
Mind matters: We studied how depression affects aspects of factual memories, say Sumantra Chattarji (right) and Bhaktee Dongaonkar.
“This is the first such study aiming to understand how depression affects a more nuanced aspect of factual memories — how information learned first is influenced by information acquired later. Importantly, this study explores this important question for the first time in Indian patient populations,” says Sumantra Chattarji from NCBS, the head of the research team. He is also the Director at the Centre for Brain Development and Repair, Bengaluru.
“Future studies can build upon these findings to examine potential changes in brain structure and function, using neuroimaging techniques such as MRI,” says Prof. Chattarji.
