To observe any effect of transcranial direct current stimulation (tDCS) on learning, memory ability and the morphology of neurons in the hippocampus and cortex of rats with cognitive impairment, and also to seek any correlation between the rats′ behavior and the thickness of the granular layer in the CA1 region of the hippocampus.

Thirty Sprague-Dawley rats were randomly divided into an observation group, a model group and a control group, each of 10. Cognitive impairment was induced in the observation and model groups by intraperitoneal injection of scopolamine, while the control group was injected with saline solution over the same period of time. After successful modeling, the observation group was given tDCS, while the model and control groups were connected with electrodes but not given any electrical stimulation. After 16 consecutive days of treatment, behavioral changes of each group were quantified using a shuttle box and a Morris water maze. On the 30th day after the mode-ling, the brains were collected to observe any changes in the morphology of the hippocampal and cortical neurons. The thickness of the hippocampal granular layer was also measured.

In the observation group the average rate of electrical impulses after the intervention [(60.5±6.67)/min] was significantly less than in the model group [(145.8±19.31)/min], while the time to find a platform was significantly shorter. The rats of the observation group also crossed the D quadrant of the platform significantly more quickly than the model group, on average. Compared with the control group, the granular layer in the CA1 region of the hippocampus [(93.47±1.07)μm] was significantly thinner on average than in the model group but compared with the model group, the observation group had significantly thicker layers [95.17±1.49)μm] on average. The thickness was negatively correlated with the number of shocks and the time to find the platform, but positively correlated with the number of crossings of the platform in the D quadrant.

The degree of impairment generated by intraperitoneal injection of scopolamine correlates with the thickness of the CA1 granular layer of the hippocampus, at least in rats. tDCS can improve the learning and memory of such rats. Its mechanism may be related to promoting structural recovery of hippocampal cortical neurons and increasing the thickness of the granular layer.

Transcranial direct current stimulation; Hippocampal cortex; Cognitive impairment; Learning; Memory