A drug that for a century has been safely used as a stain and to treat medical disorders could boost activity in brain regions linked to short-term memory and attention, results of a placebo- controlled study demonstrate.
Using functional MRI (fMRI), researchers found that a single oral dose of methylene blue increased brain activity in the bilateral insular cortex, as well as the prefrontal cortex and parietal and occipital lobes, compared with placebo.
Timothy Q. Duong, PhD, from the University of Texas Health Science Center at San Antonio, pointed out that an advantage of methylene blue is that it has been proven to be nontoxic and is “very safe.”
Dr Duong told Medscape Medical News that the drug has been available for about a century. It has been used on a long-term basis to treat methemoglobinemia and, in the emergency setting, cyanide and carbon monoxide poisoning.
He also pointed out that no other clinically approved drug is used to improve memory, making methylene blue “unique and novel in that sense.”
“I’m sure there are a couple of supplements that can claim to have some memory effects,” he said, adding that as far as he knows, these agents have not been tested in clinical trials, nor have they been approved by the US Food and Drug Administration.
The research was published online June 28 in Radiology.
In the 1970s, studies in rodents demonstrated the memory-enhancing effects of methylene blue. However, the underlying neuronal mechanisms and the drug’s impact on short-term memory and sustained attention have not been explored.
The researchers conducted a randomized, double-blinded, placebo-controlled clinical trial in which 26 healthy individuals aged 22 to 62 years were assigned to single-dose administration of methylene blue 280 mg or a blue food colorant as placebo.
The participants completed a psychomotor vigilance task to test sustained attention and a delayed match-to-sample task to measure short-term memory while undergoing fMRI, both before and 1 hour after administration of the study drug or placebo.
In addition, the impact of methylene blue on cerebrovascular reactivity was examined by determining cerebral blood flow during a carbon dioxide challenge before and after administration.
The results showed that during the psychomotor vigilance task, methylene blue was associated with significantly increased activity on fMRI in the bilateral anterior and posterior insular cortices during the attention phase (P = .01-.008).
In addition, methylene blue was associated with significantly increased fMRI activity during the short-term memory task in the bilateral occipital lobes, the basal ganglia, the thalami, the parietal lobules, the anterior cingulate gyrus, and the cerebellum (P = .03-.0003).
After administration of methylene blue, there was also an approximately 7% increase in the number of correct behavioral responses (P < .01). No change was observed in the participants who were given placebo. There were no significant changes in cerebral blood flow.
“The results support the notion that methylene blue enhances memory performance and functional MR imaging activity in brain regions associated with a visuospatial short-term memory task,” the investigators write. They note that their findings are “consistent with behavioral measurements in the same subjects.”
Highlighting the fact that the current study did not examine the impact of methylene blue on long-term memory, Dr Duong said that he and his colleagues are currently conducting a clinical trial of the drug in patients with mild cognitive impairment and Alzheimer’s disease. They will report the results early next year.
In this randomized study, low-dose methylene blue increased functional MR imaging activity during sustained attention and short-term memory tasks and potentiated memory retrieval. Specifically, the major findings showed that low-dose methylene blue increased (a) insular functional MR imaging activity during sustained attention of the psychomotor vigilance task and (b) functional MR imaging activity in the encoding, maintenance, and retrieval neural networks of the delayed match-to-sample task. These findings suggest that methylene blue can modulate certain brain networks related to sustained attention and short-term memory after a single low oral dose. At low concentrations in the brain, methylene blue acts as an electron cycler that produces regional selectivity effects in brain regions where mitochondrial respiration can accept more electrons because of increased energy demands (8,9). Accordingly, we found that methylene blue mainly produced regional functional MR imaging effects in task-related brain regions and their interacting networks.
To our knowledge, there is no previous study that suggests that low-dose methylene blue may modify sustained attention or reaction time consistent with our behavioral results. However, we found that methylene blue may still have some effect in regions of the underlying neural networks. Administration of methylene blue was associated with increased functional MR imaging activity in the bilateral anterior and posterior insular cortex during the attention phase of the psychomotor vigilance task. The insular cortex is located at the junction of the frontal, parietal, and temporal lobes and serves as a central regulatory hub that integrates motor control and sensory, autonomic, and salient stimuli, which are important for sustained attention (22,25). Multiple functional neuroimaging studies have linked attention deficits in patients with schizophrenia and bipolar disorder to abnormalities in the insular cortex (31). Our findings of an association of methylene blue intake with increased activity in the insular cortex are consistent with the hypothesis that methylene blue may modulate an important hub of active psychomotor vigilance task networks. In a previous rodent study, methylene blue potentiated stimulus-evoked functional MR imaging response in the somatosensory cortex during forepaw stimulation (8). Similarly, in our study, methylene blue potentiated stimulus-evoked functional MR imaging response in the insular cortex, which contributes to sustained attention during the psychomotor vigilance task.
During the encoding phase, there was strong activation in the bilateral inferior frontal gyri, left parahippocampal gyrus/hippocampus, right superior parietal lobule, and left inferior frontal gyrus after administration of methylene blue. Because these regions were activated during memory task encoding, this finding suggests that methylene blue potentiated frontoparietal networks that are important for encoding, such as the bilateral inferior frontal gyri and right superior parietal lobule, and limbic networks that are important for short-term memory, including the parahippocampal gyrus and hippocampus. The large clusters in bilateral inferior frontal gyri have been shown to play fundamental roles in the encoding of new memories (32,33). It is possible that improved metabolic activity within these regions as mediated by methylene blue may improve visuospatial memory retention performance, visual discrimination learning, and object recognition memory, as was previously reported in studies on rodents that were treated with methylene blue (7,11).
During the maintenance phase, there was strong activation in the bilateral posterior cerebelli, left middle and inferior frontal gyri, and right superior frontal gyrus after methylene blue administration. These clusters were previously described as being part of the visuospatial working memory network that facilitates retention of the stimulus (23,34,35). The clusters in the right superior frontal gyrus and left middle and inferior frontal gyri also correspond to areas of the dorsolateral prefrontal cortex, a key component of the working memory network (36,37).
The retrieval phase showed fewer activated regions after methylene blue administration relative to other phases of the delayed match-to-sample task. These methylene blue effects involved the right inferior frontal gyrus and the right occipital visual cortex, areas that play important roles in the visual examination of stimulus and memory retrieval (23,24). Together, these detected neuroimaging correlates of methylene blue administration may have contributed to improved visual discrimination and object recognition within the visuospatial working memory network that led to a 7% increase in behavioral performance. In short, our results suggest that, in humans, low doses of methylene blue enhance working memory processing in the brain.
Group analysis revealed no significant difference in CVR in the activated areas associated with the delayed match-to-sample and psychomotor vigilance tasks, a finding consistent with an animal functional MR imaging study that used 5% CO2 inhalation and showed that low-dose methylene blue does not affect CVR in rats (8). These findings indicate that low-dose methylene blue does not exert an observable effect on vascular reactivity in the brain. On the other hand, low-dose methylene blue increases brain oxygen consumption, as was measured with in vitro and in vivo animal models (5,8,38). Therefore, the task-based functional MR imaging signals modified by methylene blue administration may more likely be attributed to changes in tissue oxygen consumption, as would be the case if methylene blue enhanced mitochondrial respiration rather than changes in basal CBF or vascular tone (14).
There are several limitations of this study. As a proof-of-concept study, the sample size was relatively small. However, this is not unusual in multimodal functional MR imaging studies with a large number of data points. Our primary goals were to use a single low dose of methylene blue, which has been shown to improve memory in animals and humans in different memory paradigms, and investigate the neuroimaging correlates of the effects of methylene blue on neural networks (5,18). Future studies will include a larger sample and chronic methylene blue dosing. We did not measure methylene blue in the blood, but a previous study showed that methylene blue reached its maximum concentration in whole blood 1 hour after oral methylene blue administration in healthy subjects (3). It is possible that methylene blue could have age-dependent and resting-state effects; future studies will investigate these effects.
In conclusion, multimodal functional MR imaging data from this randomized, double-blinded, placebo-controlled clinical study support the hypothesis that a single low dose of methylene blue modulates functional MR imaging activity during sustained attention and working memory in the human brain. The results support the notion that methylene blue enhances memory performance and functional MR imaging activity in brain regions associated with a visuospatial short-term memory task. These findings are consistent with behavioral measurements in the same subjects. This work provides a neuroimaging foundation to pursue clinical trials of methylene blue in patients undergoing healthy aging and those with cognitive impairment, dementia, or other conditions who may benefit from drug-induced memory enhancement.