Proceedings of The Physiological Society

Physiology 2014 (London, UK) (2014) Proc Physiol Soc 31, C24

Oral Communications

Transcranial stimulation promotes consolidation of imprinted memory in domestic chicks (Gallus gallus)

A. Nicol1, B. McCabe1

1. Sub-department of Animal Behaviour, University of Cambridge, Cambridge, United Kingdom.

Domestic chicks learn the visual features of an object through imprinting, subsequently approaching that stimulus in preference to others. The intermediate medial mesopallium (IMM) stores the recognition memory of imprinting (McCabe 2013). The responses of IMM neurons are altered by imprinting: more respond to an imprinted stimulus than to an alternative. Behavioural and electrophysiological effects of imprinting are impaired if sleep is disturbed shortly after imprinting, but maintained in undisturbed chicks (Jackson et al 2008). Here we show the effect of post-training transcranial stimulation on imprinted preferences.Chicks (n=57) were hatched and reared in darkness to ~12h post-hatch, then placed in running wheels and tested to establish which of 2 rotating stimuli (red box, RB, or blue cylinder, BC) was approached preferentially before imprinting. The preference test (PT0) comprised serial exposures to the stimuli (4x2min, RB-BC-BC-RB). Under anaesthetic (0.12ml Equithesin, i.p.), 38 chicks had 2 stainless steel electrodes fitted to the frontal bones of the skull near the midline (left rostral, right caudal). Next day, they were trained by exposure to the stimulus not preferred in PT0 (2x1h sessions, 90min interval). Post-training, chicks were tested as in PT0, but with 4min presentations (PT1). They then had 6h of disrupted rest (DR) in darkness, with wheels locked. Disruption was by turning the wheel once for 60s at random in each 30min of DR. In the first 3h of DR, chicks received: slow wave (0.75Hz, n=12, SW chicks) or theta frequency (6Hz, n=9, TF chicks) stimulation (~2μA peak-peak, sinusoidal), or no stimulation (17 sham implanted, and 19 non-implanted controls). Preferences were again tested ~8h (PT2) and ~16h (PT3) after the end of DR.The chicks did not differ significantly by group at PT0 or PT1. Mean preference scores (% approach to TS) at PT1 (73.0±2.0% sem) were higher (anova, P=0.001) than at PT0 (39.8±2.0%), i.e. chicks were imprinted. There was no significant difference between scores in PT2 and PT3, so these were pooled (PT2-3). Scores at PT2-3 for SW and TF chicks (73.2±3.1%) did not differ significantly from those at PT1. In sham and control chicks (unstimulated) the scores fell (anova, P=0.004, 64.1±3.0%). The 2 unstimulated groups of chicks did not differ significantly in any test. In a control experiment, the behavioural activity of SW, TF and unstimulated chicks (n = 4, 4, and 16 chicks respectively) in unlocked wheels during undisturbed rest did not differ, indicating similar arousal across groups.The results show that memory for the imprinted stimulus is protected by SW or TF transcranial stimulation from attenuation otherwise resulting from disturbance during DR. This is reminiscent of improved memory in human subjects following SW transcranial stimulation during sleep (Marshall et al 2004).

Where applicable, experiments conform with Society ethical requirements