Establishment and transfer of classical eyeblink conditioning using electrical microstimulation of the hippocampus as the conditioned stimulus
Fig 1
(A) Diagram of EBC measurement. The upper left eyelid movements were measured by a high-resolution spring-return potentiometer that was attached via a thread lead hooked with a nylon loop, which was sutured into the left upper eyelid. Bipolar electrodes were implanted in the right hippocampus (Hip). Electrical stimulation of right hippocampus (Hip-CS) or auditory stimulation (pure tone) was used as the conditioned stimulus (CS). Air-puff presented to the left cornea was used as the unconditioned stimulus (US). (B) Diagram of the sagittal section of a guinea pig brain, showing the electrical stimulation sites. (C, D) Schematic diagrams illustrate the temporal relationship between CS and US and analysis periods of CR and UR in delay (C) and trace (D) paradigms. In delay paradigm, US co-terminated with the offset of CS; and in trace paradigm, a stimulus-free trace interval of 250 ms was interposed between the CS offset and the US onset. The durations of CS and US were 350 ms and 100 ms, respectively. In each trial, parameters of the conditioned eyeblink response (CR; 50–250 ms period after the CS onset) and unconditioned eyeblink response (UR; 0–300 ms period after the US onset) were analyzed. These responses were defined based on the average magnitude of the baseline (a 0~800 ms period prior to the onset of the CS).