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A Variable Oscillator Underlies the Measurement of Time Intervals in the Rostral Medial Prefrontal Cortex during Classical Eyeblink Conditioning in Rabbits

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2015-11-04
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Society for Neuroscience
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We were interested in determining whether rostral medial prefrontal cortex (rmPFC) neurons participate in the measurement of conditioned stimulus– unconditioned stimulus (CS-US) time intervals during classical eyeblink conditioning. Rabbits were conditioned with a delay paradigm consisting of a tone as CS. The CS started 50, 250, 500, 1000, or 2000msbefore and coterminated with an air puff (100 ms) directed at the cornea as the US. Eyelid movements were recorded with the magnetic search coil technique and the EMG activity of the orbicularis oculi muscle. Firing activities of rmPFC neurons were recorded across conditioning sessions. Reflex and conditioned eyelid responses presented a dominant oscillatory frequency of 12 Hz. The firing rate of each recorded neuron presented a single peak of activity with a frequency dependent on the CS-US interval (i.e., 12 Hz for 250 ms, 6 Hz for 500 ms, and 3 Hz for 1000 ms). Interestingly, rmPFC neurons presented their dominant firing peaks at three precise times evenly distributed with respect to CS start and also depending on the duration of the CS-US interval (only for intervals of 250, 500, and 1000 ms). No significant neural responses were recorded at very short (50 ms) or long (2000 ms) CS-US intervals. rmPFC neurons seem not to encode the oscillatory properties characterizing conditioned eyelid responses in rabbits, but are probably involved in the determination of CS-US intervals of an intermediate range (250 –1000 ms). We propose that a variable oscillator underlies the generation of working memories in rabbits.
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En este estudio se explica cómo las neuronas de la corteza prefrontal rostro medial (rmPFC) participan en la medición de los intervalos de tiempo entre los estímulos condicionado e incondicionado (CS-US) durante el condicionamiento clásico del reflejo palpebral. La tasa de activación de cada neurona registrada presentó un sólo pico de actividad con una frecuencia dependiente del intervalo CS-US (es decir, ≈ 12 Hz durante 250 ms, ≈ 6 Hz durante 500 ms y ≈ 3 Hz durante 1000 ms). Curiosamente, las neuronas rmPFC presentaron sus picos de disparo dominantes en tres tiempos precisos distribuidos uniformemente con respecto al inicio del CS, y también dependiendo de la duración del intervalo CS-US (sólo para intervalos de 250, 500 y 1000 ms). Las neuronas rmPFC parecen no codificar las propiedades oscilatorias que caracterizan las respuestas condicionadas de los párpados en conejos, pero probablemente están involucradas en la determinación de los intervalos CS-US de un rango intermedio (250-1000 ms). Esto permitió proponer que un oscilador variable subyace a la generación de memorias de trabajo en conejos.
Proyectos de investigación MINECO-BFU2014-56692-R BIO122/CVI-2487 BIO122/P07-CVI-02686
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Journal of Neuroscience, vol. 35, nº 44, p. 14809-14821
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