Effects on declarative memory via bilateral transcranial direct current stimulation (tDCS) over parietal and temporal cortices

Die transkranielle Gleichstromstimulation (tDCS) erwies sich in der bisherigen Grundlagenforschung als bewährte Methode zur Aufschlüsselung von komplexen kognitiven Funktionen. Bisher deuten bildgebende Verfahren auf ein Zusammenwirken parietaler und temporaler Kortizes beim Rekognitionsprozess deklarativer Gedächtnisinhalte hin. In der vorliegenden Arbeit sollten nun die Auswirkungen einer bilateral temporal und parietal applizierten tDCS auf die deklarative Gedächtnisleistung während der Rekognition untersucht werden. Unter Verwendung eines einfach-blinden, kontrollierten und randomisierten Studiendesigns wurden junge, gesunde Probanden drei voneinander unabhängigen, hinsichtlich der individuellen Gedächtniskapazität ausgeglichenen Studiengruppen für Placebo-, parietale und temporale Stimulation zugeordnet. Während der Bearbeitung eines computergestützten Alt-Neu-Rekognitions-Paradigmas erhielten zwei Gruppen bilaterale tDCS mit linkshemisphärischer a-tDCS über dem parietalen bzw. temporalen Kortex und eine Gruppe Placebo-Stimulation. Zielsetzend wurde die Einflussnahme der tDCS auf die deklarative Rekognitionsleistung bezüglich verbaler Gedächtnisinformationen gemessen. Eine Verbesserung der deklarativen Rekognitionsleistung äußerte sich in höheren Trennschärfeindex- und Treffgenauigkeitswerten der beiden verumstimulierten Gruppen im Vergleich zur Placebo-stimulierten Gruppe. Ein konträres Dissoziationsmuster zeigte sich insofern, als die temporale Stimulationsgruppe eine signifikant höhere Treffgenauigkeit bei der Rekognition alter Items im Vergleich zu neuen aufwies und die parietale Stimulationsgruppe mit einer signifikant höheren Treffgenauigkeit neue Items im Vergleich zu alten wiedererkannte. Diese Ergebnisse unterstreichen die Involvierung der temporalen und parietalen Hirnareale in möglicherweise unterschiedliche Stadien des Rekognitionsprozesses deklarativer Gedächtnisinhalte

The summary of the fixed effects of the final model taking reaction-time as dependent variable (N = 5691; log-likelihood = -39621).

<p>Note: Random effect for subject intercept had SD of 148.7. SE: standard error of mean; df: degrees of freedom.</p><p>The summary of the fixed effects of the final model taking reaction-time as dependent variable (N = 5691; log-likelihood = -39621).</p

The experimental procedure for the encoding A) and for the recognition B) phase of the verbal learning task.

<p>The experimental procedure for the encoding A) and for the recognition B) phase of the verbal learning task.</p

The summary of the fixed effects of the final model taking confidence rating as dependent variable (N = 7787; log-likelihood = 35888).

<p>Note: Random effect for subject intercept had SD of 12.49. SE: standard error of mean; df: degrees of freedom.</p><p>The summary of the fixed effects of the final model taking confidence rating as dependent variable (N = 7787; log-likelihood = 35888).</p

The summary of the fixed effects of the final model taking accuracy as dependent variable (N = 8448; log-likelihood = -5269.6).

<p>Note: Random effect for subject intercept had SD of 0.16. SE: standard error of mean.</p><p>The summary of the fixed effects of the final model taking accuracy as dependent variable (N = 8448; log-likelihood = -5269.6).</p

The mean accuracies (%) were significantly higher for both the parietal and the temporal groups compared with the sham stimulation group.

<p>Error bars represent standard error of the mean. Asterisks indicate significant differences.</p

D’ values were significantly and marginally higher for the temporal and parietal groups respectively, compared with the sham stimulation group.

<p>D’ value is zero at random choice. Error bars represent standard error of the mean. Asterisk indicates significant differences; the plus sign indicates marginally significant differences.</p

Separating recognition processes of declarative memory via anodal tDCS: boosting old item recognition by temporal and new item detection by parietal stimulation.

There is emerging evidence from imaging studies that parietal and temporal cortices act together to achieve successful recognition of declarative information; nevertheless, the precise role of these regions remains elusive. To evaluate the role of these brain areas in declarative memory retrieval, we applied bilateral tDCS, with anode over the left and cathode over the right parietal or temporal cortices separately, during the recognition phase of a verbal learning paradigm using a balanced old-new decision task. In a parallel group design, we tested three different groups of healthy adults, matched for demographic and neurocognitive status: two groups received bilateral active stimulation of either the parietal or the temporal cortex, while a third group received sham stimulation. Accuracy, discriminability index (d') and reaction times of recognition memory performance were measurements of interest. The d' sensitivity index and accuracy percentage improved in both active stimulation groups, as compared with the sham one, while reaction times remained unaffected. Moreover, the analysis of accuracy revealed a different effect of tDCS for old and new item recognition. While the temporal group showed enhanced performance for old item recognition, the parietal group was better at correctly recognising new ones. Our results support an active role of both of these areas in memory retrieval, possibly underpinning different stages of the recognition process