My grandmother spent the last several months of her life confined to a hospital bed in a vegetative state. Diabetes had taken her eyesight long before, and her mind had been disintegrating for years. Shortly before Abuela died, she looked me in the eye and asked me if I had any children (I told her did not). It was in that moment that I realized I was going to lose her, which hurt even more than her failing to recognize me. Near the end, she appeared submerged in deep sleep punctuated by rare flashes of lucidity. Each time her awareness returned I hoped for a permanent improvement, but her mind was just coming up for air before diving ever deeper.

I was living in the US at the time, but flew back to Spain to see my grandmother whenever I could, which was not often enough. The sparks of clarity where she recognized me as her oldest grandchild are now precious memories (even if not all of them are positive and heartwarming – my grandmother suffered before she went). I treasure each and every one of those interactions, and will never forget them.

My sister, who lived in the same town as Abuela, had similarly meaningful moments with her during those last months—probably more than I did, because she was able to visit every other day. Although some of the memories are painful to my sister, she shared them with me over the years, for which I’m grateful. Except for one memory. One story was particularly upsetting to me, and although I never complained, I wished she had not told it to me.

Years after my sister first told me about this interaction, she described it to me again. Hearing it anew, I realized that I had somehow managed to forget all about it. And I immediately wished that I could forget it for a second time, but knew that the memory was now there to stay. I was wrong. It’s been several years since this last conversation with my sister, and for the life of me I can’t remember the story.

I know that it was horrible and that it disturbed me, and I assume it had something to do with my grandmother experiencing physical or psychological pain. But that’s just an educated guess. The content of the memory itself is gone. Again. Thankfully.

Or is it? Have I suppressed my conscious memory of the tale (twice!) but left an unconscious trace of it lurking beneath my awareness?

Research studies have shown that people can reduce the conscious recall of unwanted memories by refusing to remember them. Voluntary suppression of retrieval reduces activity in the hippocampus, a brain structure critical to memory formation. But until recently, it was not known whether the suppressed information could persist, in unconscious form, and – at least according to psychoanalytic theory—lead to untold mental problems later on.

In a PNAS study published last year, neuroscientist Pierre Gagnepain and his colleagues set out to determine whether suppressed memories can affect our perception in ways that escape our awareness. To find out, they asked experimental subjects to memorize written words (for instance, “duty”) paired with object pictures (for instance, a pair of binoculars). Then, the experiment proper started. On “think” trials, subjects had to recall the paired objects that went with the word cues. On “no-think” trials, subjects had to prevent the objects from entering their conscious awareness. Experimenters asked subjects “not to generate distracting thoughts, but to focus on the reminder, and to suppress the object from awareness if it intruded.” At the same time, they scanned the subjects’ brains with functional MRI.

Once the subjects completed the think/no-think trials, the scientists asked them to identify objects that were presented amid visual noise. The idea was to find out if suppressed objects might be harder to detect than non-suppressed objects. Again, they scanned the subjects’ brains while they performed this task.

The results showed that suppressing memories impaired visual perception later on. Subjects found the suppressed objects harder to tell apart from noise than other objects that they had also encountered recently, but which they had not actively suppressed. The brain imaging results pointed to a neural mechanism mediated by the frontal cortex, which appears to suppress intrusive visual memories by inhibiting activity in the visual cortex.

The research was limited to simple visual memories, but the general mechanisms could in principle apply to other forms of motivated forgetting. If so, there may be important clinical implications: people often suppress intrusive traumatic memories from their awareness, but until now it wasn’t clear that it is wise to do so.

The study by Gagnepain and his colleagues shows that expunging a memory from conscious retention also disrupts its unconscious expression. In other words, we should feel free to try and force ourselves to forget: our unwanted memories do not appear to creep around in our unconscious and won’t come back to bite us.

And with that, one last word to my sister, in case she’s reading this.

Carolina, I love you and you know how much I loved our grandmother. But please don’t tell me the deathbed story again. Now that I’ve written about it, I know that no amount of willpower will make me forget it a third time. So don’t remind me. I’m so sorry for whatever happened… but truly I don’t want to know.