ORIGINAL PAPER J. Erber á B. Pribbenow á J. Kisch á D. Faensen Operant conditioning of antennal muscle activity in the honey bee (Apis mellifera L.) Accepted: 29 March 2000 Abstract Antennal movements of the honey bee can be conditioned operantly under laboratory conditions. Using this behavioural paradigm we have developed a preparation in which the activity of a single antennal muscle has been operantly conditioned. This muscle, the fast ¯agellum ¯exor muscle, is innervated by an identi- ®ed motoneuron whose action potentials correlate 1:1 with the muscle potentials. The activity of the fast ¯a- gellum ¯exor muscle was recorded extracellularly from the scapus of the antenna. The animal was rewarded with a drop of sucrose solution whenever the muscle activity exceeded a de®ned reward threshold. The re- ward threshold was one standard deviation above the mean spontaneous frequency prior to conditioning. Af- ter ten conditioning trials, the frequency of the muscle potentials had increased signi®cantly compared to the spontaneous frequency. The conditioned changes of frequency were observed for 30 min after conditioning. No signi®cant changes of the frequency were found in the yoke control group. The ®ring pattern of the muscle potentials did not change signi®cantly after conditioning or feeding. Fixing the antennal joints reduces or abol- ishes associative operant conditioning. The conditioned changes of the frequency of muscle potentials in the freely moving antenna are directly comparable to the behavioural changes during operant conditioning. Key words Honey bee á Operant learning á Antennal system á Neural correlate of learning Abbreviations CI conditioning index á ISTH interspike time interval histogram á PER proboscis extension response á TH time histogram Introduction Bees can be conditioned classically to a variety of sensory cues under laboratory conditions (for a review see Menzel and MuÈller 1996). The best-known learning paradigm is conditioning of the proboscis extension response (PER) to an odour. Using the PER, bees can also be conditioned very rapidly to other sensory cues. They can learn to dis- criminate between tactile patterns which dier in surface structure, size, form and position (Erber et al. 1998). Acquisition of a tactile pattern is similarly ecient and rapid as olfactory learning (Scheiner et al. 1999). Tactile conditioning under laboratory conditions also involves operant behaviour, because the bees must scan the tactile pattern actively to associate it with a reward. Recently, an operant learning paradigm which makes use of the active antennal scanning movements was de- veloped for the laboratory (Kisch and Erber 1999). In these experiments, the contacts of one antenna with two objects placed ventrally and dorsally are measured electronically. During the conditioning phase the bee is rewarded with sucrose solution whenever the frequency of contacts for either objects exceeds a de®ned reward threshold. This threshold is one or two standard devia- tions above the spontaneous contact frequency prior to conditioning. After ten rewards, the bees make signi®- cantly more contacts with the rewarded object than with the unrewarded alternative. Yoke controls, which were rewarded irrespective of the momentary contact behav- iour, did not show this conditioned increase. These ex- periments demonstrated that bees can operantly learn to associate antennal motor activity and positional infor- mation with rewards. The motor system of the bee antenna has been analysed in detail in the last few years (Kloppenburg 1995; Pribbenow and Erber 1996; Erber et al. 1997). Antennal movements of the bee are controlled by six muscles. Four muscles in the head enable rotatory movements of the scapus in the ball and socket joint between the head capsule and the scapus. The ¯agellum J Comp Physiol A (2000) 186: 557±565 Ó Springer-Verlag 2000 J. Erber (&) á B. Pribbenow á J. Kisch á D. Faensen Institut fuÈr O È kologie und Biologie, Technische UniversitaÈt Berlin, Franklinstr. 28/29, D-10587 Berlin, Germany e-mail: nevr2134@mailszrz.zrz.tu-berlin.de Tel.: +49-30-314-73344; Fax: +49-30-314-73177