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To see if anodal and cathodal stimulation by transcranial direct current stimulation (tDCS) of the left dorsolateral prefrontal cortex (DLPFC) affects memory during the encoding (learning) phase and the retrieval (recall) phase.

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The study could have been done as a between subject study design in order to prevent people memorising the task.

Randomised order of participants helped with reducing the memorising of the task and order of stimulation.

Anodal improved memory for encoding and trend for recognition for verbal memorisation

Cathodal impaired for both encoding and recognition verbal memorisation

Location specific and polarity specific.

Limitations - exact functional role for tdcs remains unclear

Stimulation of the right and side may have been better and needs further study

TDCS is highly selective to certain brain area

TDCS reliant on the other study for the length of time of effect after stimulation

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Within subject design of 32 participants from a UK university – av age 22. Right handed, normal vision, no neurological/psychiatric issues, no medication. Engaged in two experiments.

The first experiment involved having tDCS anodal, cathodal and sham on the left DLPFC and a control on another part of the brain (primary motor cortex) stimulation during the encoding part of the experiment. These 4 trials were carried out with 48 hours in-between to minimize carry over effects.

They were shown 4 sets of 30 words (had 5 to start as a practice) and had to memorize them by visualizing the words whilst also judging the number of syllables in the word with their left hand. They then had a 60-minute interval, watching TV etc. and then had to recall the words by looking at pairs of words, one which they had seen and one they had not, they had to say which one they had seen earlier as quickly and accurately as they could. Participants were then given a percentage of accuracy.

Experiment 2 was the same but carried out with a different set of participants but the 3 trial stimulations (no control) were carried out in the retrieval phase of the experiment rather than the encoding phase.

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Tried limit the obstacles of with-in study design by changing the order in which participants did the task to control for task improvement based on experience

Changed words in the memorisation task to avoid familiarity

Small sample(?)

Participants weren't assessed on cognitive abilities or baseline memory

tDCS is not that precise, can stimulate large areas of the brain

Low ecological validity due to word memorisation task - doesn't represent memory in the real world (could've incorporated more realistic memory tasks)

Doing a between study would have controlled for some of the aforementioned limitations

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2 experiments with 32 participants

Right handed

All had good vision or wore glasses

Mean age 22 years

Given a memory test with a range of words

Experimental design

Within subjects design (to save money)

Looked for causation not correlation

Group 1 had stimulated during encoding

Group 2 had stimulating during recognition

Then groups swapped but the order was randomised to reduce practice effects

Measured learning speed and learning success

Participants who received anodal stimulation saw an improvement in their memory

But participants saw a decrease in memory after cathodal stimulation. This was also true for the sham group

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No control group

Small sample

Cathodal and anodal stimulation are influenced by many different factors including:

Results difficult to repeat -

Stimulation intensity and duration

What was the long term follow up? Effects only noted after 2 hours - Were the effects gone? Notable - participant care

Passed the ethics committee!

NSE as a sole marker -

Results difficult to repeat - Electrode placement makes a huge difference

Passed the ethics committee

NSE as a sole marker to determine safety of experiment.

The ecological validity - task doesn't relate to everyday life.

TCS/ TMS - TMS (single pulse is more specific so you know which area you are stimulating)

TCS is not as specific.

Stimulation techniques vary. TMS is

Causality can be ascertained however, the specify of the location is more broad.

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Methods used:

The goal was to induce prolonged motor cortical excitability reductions by transcranial direct current stimulation in the human brain.

Researchers used a between subjects design. The IV was time spent under stimulation. The DV was the cortical excitement (how long the effects of stimulation lasted for).

A randomised repeated measurement design involving  12 participants (9 of which were female – mean age 22.5). They applied a Cathodal direct transcranial current stimulation to the hand area of the primary motor cortex. From 5 to 9 min in separate sessions.

Cortico-spinal excitability was tested by single pulse transcranial magnetic stimulation.

Transcranial electrical stimulation and H-reflexes were used to learn about the origin of the excitability changes. Neuro Stimulation Enzyme (NSE)  factors (a serum)  were used to monitor for safety.

Findings

A two way ANOVA on the initial 15 min of recovery revealed a significant main effect of TIME after polarisation.

Five and 7 min direct current stimulation resulted in motor cortical excitability reductions, which lasted for minutes after the end of the actual stimulation.

9 min stimulation induced after-effects for up to an hour after the end of stimulation, as revealed by transcranial magnetic stimulation.

Muscle evoked potentials elicited by transcranial electric stimulation and H-reflexes did not change.

Neurone specific enolase concentrations remained stable throughout the experiments.

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An experiment, between groups. Different levels of stimulation for each group. Apply stimulus to see if would excite the motocortical

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An experiment, between groups. Different levels of stimulation for each group. Apply stimulus to see if would excite the motocortical

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32 participants, 19 females. 2 experimental groups - 1. Encoding 2. Recognition

They were fluent English/right-handed /normal vision/no medication.

Experimental design: with in subject design- same person to different conditions. Single blind cortical site control. 1st stimulated during 2nd half of encoding phase- 4 sessions.

2nd stimulated during second half of recognition. Each session had different stimulus. IV: Left anodal/ cathodal/ sham(short time electrical current/single bias) control group. / 4 blocks dv: when stimulated- number of words.

working memory control memory/improvement.

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first critique that comes to mind is why such a specific part of the brain was used as the stimulation could have been affected by other parts of the brain not just the DLPFC.

Doesn't indicate a long term memory change- experiment was short term. Talk about long term but don't mention it.

Not many benefits of the cathodal, more all about the anodal.

Limiting study, some level of improvement but don't reach significance level.

first experiment was significant and the second not significant- sample size could have been too small. Future research should be done again but use both sides- not just the left

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Participants are very young- could extend to other age ranges.

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small sample size 12 people, placebo is excluded? 2 sets of experiments conducted. Placebo group not used. Issues with ethics. Because there is an stimulus it is possible to say there is causation.

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small sample size 12 people, placebo is excluded? 2 sets of experiments conducted. Placebo group not used. Issues with ethics. Because there is an stimulus it is possible to say there is causation.

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Word memorize task- not relatable to everyday life. Not real memories- artificial task- validity issue.

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Aim was to see how it helps stroke patients, but why didn't they use stroke patients.

learning typical brain functions but should have include another condition.