Journal of Comparative and Physiological Psychology 1964, Vol. 58, No. 3, 423-426 RELATIONSHIPS BETWEEN HEART RATE AND OPEN-FIELD BEHAVIOR 1 CHARLES T. SNOWDON, 2 DONNA D. BELL, 3 AND NORMAN D. HENDERSON Oberlin College 64 Wistar rats were reared under either enriched or deprived conditions. In adulthood, heart rate, defecation, and ambulation were recorded in an open field. Restricted Ss were more emotional and had lower heart rates than Ss raised in enriched environments. Low heart rate was consistently associated with indices of heightened emotionality, low activity, and increased defeca- tion. Two of the most widely used indices of emotionality in lower animals are the amount of defecation and the activity or ambulation of Ss in a strange situation. However, the validity of these measures has never been clearly established, and there remains a variety of opinions (e.g., Broadhurst, 1960; Tobach & Schneirla, 1962) concerning the relative merits of each as an index of emotional arousal. Because of the lack of clear external cri- teria of emotionality, one is primarily faced with a problem of construct valida- tion. In general, defecation increases and ambulation decreases when Ss are placed in a situation thought to be emotionally arousing, and upon repeated testing these reactions tend to become less pronounced. Although defecation is linked to autonomic reactions and evidence exists concerning the relationship between extreme fear and eliminative responses in humans (Hall, 1938; Stouffer, Guttman, Suchman, Lazars- feld, Star, & Clausen, 1950), there is little work directly measuring relationships be- tween open-field behavior and the activity of the autonomic nervous system. Since such data would appear valuable for vali- dating behavioral measures of emotionality, the following investigation was carried out to determine whether significant relation- ships exist between heart rate and defeca- tion-ambulation indices of emotionality in rats. It has been found that rats reared in enriched environments are generally less 1 This research was supported by Grants G21447 and G22812 from the National Science Founda- tion. 2 Now at the University of Pennsylvania. 3 Now at the University of California, Berkeley. emotional than Ss reared in relative depri- vation (e.g., Denenberg & Morton, 1962; Levine, 1956). Therefore, in the present investigation Ss were reared in either en- riched or restricted environments before testing, in order to increase heterogeneity of emotional behavior and to provide group comparisons on the activity, heartbeat, and defecation measures. METHOD Subjects The /Ss were 32 male and 32 female Wistar rats, born on shavings, weaned at 21 days, and main- tained on Purina lab chow and water ad lib. Apparatus The behavioral testing apparatus consisted of an open field 36 in. square with 24-in. high walls painted flat black. The floor was covered with white plastic and divided into four 18-in. quadrants by means of two photoelectric beams intersecting at right angles. The number of times S crossed these beams was automatically recorded on an electric counter, the total counts being considered S's activity score. Suspended 18 in. above the center of the field was a 150-w. red reflector floodlamp, which provided an illumination of 100 ft-c in the center and 40 ft-c along the walls. Heart rate records were taken in a copper shielded, relatively soundproofed box 30 X 30 X 18 in. A 75-w. flood- lamp placed outside the copper screening illumi- nated the interior of the box through a hole in the center of the lid. Two additional holes in the lid enabled Es to observe S at all times. The S's im- planted electrodes were attached to light No. 30 wires suspended from the top of the box, which led to an E & M physiograph, where heartbeats were amplified and recorded. Experimental Design and Procedure A 2 X 2 factorial design with 16 Ss per cell was used with sex and treatment (enriched vs. re- stricted) being the two major factors. At weaning 423