Have you ever had a "senior moment" when your memory fails unexpectedly?   Though it can happen at any age, it can often be an uncomfortable reminder that you are getting older.

Long recognized as an inevitable part of the aging process, most seniors tend to laugh these lapses off. Still, a slow decline in mental and physical functioning can seriously compromise quality of life, especially if it leads to neurodegenerative conditions such as Alzheimer's disease.  

And this is a problem that affects everybody.   As the Baby Boom generation grows older, we are seeing a rapid growth in the number of seniors worldwide.  By 2050, the number of adults over the age of 65 is expected to outnumber children by two to one. Though advances in geriatric care, improved public health measures, and rising standards of living are allowing people to live longer and more productively, the health care systems in most countries are already falling behind in the services available for many seniors, especially seniors suffering from dementia.

As part of a worldwide research initiative, geriatric researchers have been studying how the brain changes with age and how to prevent the devastating loss of cognitive functioning  seen in many seniors.  Still, in studying how memory and cognition can decline as we grow older,  it is important to recognize that not all cognitive abilities will decline at the same rate. Working memory, usually defined as the ability to hold, process, and manipulate information on a short-term basis, seems especially vulnerable to aging (particularly after the seventh decade of life). Then there is long-term episodic memory or the recall of autobiographical information which can also be affected by aging.

Brain imaging research has shown that aging produces key changes in the brain including the thinning of gray matter in the cortex, decreased density of white matter fibers, expanding ventricles, depletion of essential neurotransmitters, and changes in brain networks.  Some regions of the brain seem to be more affected than others however and, not surprisingly, those regions of the brain linked to working memory seem to show the greatest changes due to age. These include the dorsolateral prefrontal cortex, the superior parietal lobe, and the medial temporal lobe, all of which play a critical role in the encoding, storage, and retrieval of memories.  

Along with the slow loss of cognitive functioning linked to aging, the aging brain can also become much more vulnerable to injury or disease.  Concussions or other forms of brain damage can affect cognitive functioning at any age but younger brains can usually recover due to greater neuroplasticity.  In older adults, this kind of brain damage can be much more serious and can often act as triggers for the development of dementias such as Alzheimer's disease or vascular dementia.

But are there ways of protecting the aging brain and preventing the loss of cognitive functioning?   Along with pharmacological research to find medications that can prevent memory loss in seniors,  other approaches are already showing promise. Exercise, for example, has been shown to have a small but significant impact on improved mental functioning in seniors while cognitive training programs can also improve working memory and executive functioning.  

But a new approach to improving cognitive functioning in seniors may well prove to be even more effective. Non-invasive brain stimulation (NIBS) techniques have already been used in treating depression, aiding neuro-rehabilitation following stroke, and in treating different psychiatric or neurological conditions. Though there is some controversy over how "non-invasive"  these techniques really are, their potential value in boosting memory in older adults is just beginning to be explored.

The two main techniques available for human brain stimulation are transcranial direct current stimulation (TDCS) and transcranial magnetic stimulation (TMS).

The first of these techniques, TDCS, uses a pair of electrodes delivering low currents to specific regions of the brain.  The rationale for TDCS is that using current in this manner will created an electric field which modifies the polarization of the resting membrane which either increases or decreases neural activity according to the polarity of the current.   In a typical TDCS trial, a participant completes a cognitive task to establish a baseline.   Then the current is administered for ten to twenty minutes after which the task is completed a second time to see if there is any improvement.  

Depending on the polarity of the current used, TDCS can either lead to improved or worsened performance though the size of the effect usually varies depending on the amount of current used and the duration of the stimulation.   While critics have compared TDCS to much cruder methods such as electroconvulsive therapy (ECT),  the only adverse effects detected to date have been headaches and itchiness at the site of stimulation so long as proper safety protocols are followed.

The other main technique, transcranial magnetic stimulation (TMS), involves using an electrical coil held above the head.  When a current is passed through the coil, a magnetic field is produced which causes a secondary electrical current in specific regions of the brain depending on where the coil is placed.  The effect of this secondary electrical current can either increase or decrease neural activity depending on how and where the magnetic field is applied.  TMS can be administered either in the form of a single pulse or repeatedly and tends to be much more expensive than TDCS though its effect is also more powerful.   

As far as cognitive stimulation is concerned, the effects of both TDCS and TMS can persist for quite some time after the stimulation takes place.  These after-effects can be important in determining whether this kind of brain stimulation can improve cognitive functioning in elderly adults and how long the benefits can last.   

In a new overview published in the journal European Psychologist, David Bartres-Fez of the University of Barcelona and Didac Vidal-Pineiro of the University of Oslo examined eight recent studies showing significant improvement of memory functioning in older adults, usually involving stimulation of the prefrontal cortex or related regions.  

But memory isn't the only brain function that can be meaningfully boosted using brain stimulation.  Along with improvement in working memory, researchers have also found evidence of improved language functioning, motor learning, and overall cognitive flexibility, including in older adults suffering from cognitive impairments.  

Though all of the studies completed so far have focused on improving brain functioning in the laboratory, there is also growing evidence that the benefits of brain stimulation can persist much longer than expected.  In healthy older individuals undergoing TDCS or TMS, the effects can last for weeks depending on which regions of the brain are stimulated.   Research looking at older adults suffering from Alzheimer's disease suggests that multiple TCDS sessions over five days can lead to improved memory functioning for up to four weeks afterward.   

While more research is definitely needed to investigate the most effective brain stimulation strategies, including possibly combining brain stimulation with brain training programs, therapists are already exploring practical applications for this new technology.   Of the techniques available so far, TDCS tends to be more popular, primarily because the equipment required is less expensive and more portable than with TMS.    Both forms of brain stimulation, along with other methods still being developed will likely continue to play an important role in therapy and research.

Brain stimulation research is still in its infancy but we will likely be hearing far more about how it can benefit older adults soon enough.   Assuming it lives up to its early promise, the future prospects seem downright electrifying.

References

Noninvasive brain stimulation for the study of memory enhancement in aging.   By Bartrés-Faz, David; Vidal-Piñeiro, Didac, European Psychologist, Vol 21(1), 2016, 41-54.  

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