Corrugator and startle responses predict memory for emotional pictures: differential effects by emotion category Michelle M. Wirth, Roxanne M. Monticelli, Daren C. Jackson, Anand Lakshmanan, and Heather C. Abercrombie Departments of Psychology and Psychiatry, University of Wisconsin - Madison DISCUSSION Our findings show that stimulus valence affects the relationship between startle and memory differently than between corrugator and memory. In particular, pleasant stimuli that are later remembered elicit more startle activity but less corrugator activity (pleasant picture effects confirmed by post-hoc comparisons.) Corrugator and startle have been shown to track negative affect and valence properties of stimuli. (Bradley et al., 2001) Emotional enhancement of memory seems to depend on arousal properties of stimuli. However, our data suggest that emotional enhancement of memory involves a combination of arousal and valence. Prior evidence implicates the amygdala in both emotion-potentiated startle (Davis, 1986) and emotional enhancement of memory / emotional learning (LeDoux, 1992). Our data are suggestive of overlapping but distinct neural systems underlying enhancement of memory by positive / pleasant vs. negative / unpleasant stimuli. Brain imaging and animal work is needed to help elucidate this hypothesis. METHODS, cont. RESULTS BACKGROUND Emotional stimuli and events are remembered better than neutral stimuli / events. In particular, it has been found that emotionally arousing stimuli are remembered better than non-arousing stimuli. (Bradley et al., 1992) Corrugator (frown) muscle activity and startle (eyeblink reflex) responses are responsive to emotional state or emotional content of a stimulus. (Bradley et al., 2001) Corrugator and startle responses tend to be intensified by negative affect and unpleasant stimuli, and lessened by positive affect / pleasant stimuli. In this study, we investigated the relationship between corrugator and startle responses to emotional visual stimuli and participants’ later memory for those stimuli. Subjects remembered more emotional than neutral words, replicating past literature (also more unpleasant than pleasant words). Picture valence affected startle and corrugator responses, also replicating past literature. After encoding, participants performed a speech stressor task to investigate other hypotheses (see Abercrombie et al., 2006). RETRIEVAL SESSION occurred 2 days after the first (“encoding”) session. Participants first performed a free recall test, followed by recognition tests (with 63 targets and 63 equivalent distractor stimuli.) 4 participants excluded for incomplete free recall data and 4 for insufficient valid startle trials (see below), leaving a sample of 44. Psychophysiology Psychophysiology data collection modeled after Jackson et al., 2000. Miniature Ag/AgCl electrodes placed for collection of EMG data from corrugator supercilii and orbicularis oculi according to Tassinary and Cacioppo (2000). Data amplified using a gain of 10,000, highpass filter 1 Hz, sampling rate 1000 Hz. Startle: lowpass filter 800 Hz; corrugator: lowpass filter 400 Hz. Startle eyeblink data integrated and rectified using a Coulbourn S76-01 contour-following integrator with a time constant of 20 ms. Startle trials were excluded if they contained excessive noise, or if the onset of the eyeblink began less than 15 ms after the startle probe. Only participants who had at least two trials free from excessive noise per probe time per picture valence were included in analyses. (4 participants were excluded.) Startle blink magnitudes (mV) = (max peak integrated EMG btwn 20 – 120 ms from probe onset) minus (amount of integrated EMG at reflex onset). Noise-free trials with no perceptible eyeblink reflex were given a magnitude of zero. Blink magnitudes Z-transformed within-subjects. Startle blink magnitudes were collapsed over probe time within subjects for each cell in the present analyses (e.g., for remembered pleasant pictures). Corrugator data were scored for artifact. A fast Hartley transform (FHT) was performed on all artifact-free 1.024-s chunks of data (extracted through overlapping Hamming windows) to derive estimates of spectral power density (mV2) in the 45–200-Hz frequency band. These values were log-transformed to normalize the data. Corrugator data divided into epochs: baseline (containing activity averaged over 2 seconds during ITI prior to picture onset) and early-picture (containing activity averaged over 3 seconds after picture onset). Corrugator reactivity to pictures was calculated by subtracting baseline score from early-picture score for a given trial. For startle, there was an overall effect of memory: Remembered pictures were associated with more startle activity than forgotten pictures, across valences. (Main effect of memory, F(1,43)=8.010 p=0.007) METHODS 61 male participants recruited to study effects of emotion-related physiology on memory. 9 excluded due to failing to show up for memory session or experimenter error. Final samples 44 and 19 (see below). PROCEDURE Participants completed 2 sessions (“encoding” and “retrieval”). ENCODING SESSION: participants viewed pleasant, neutral, and unpleasant IAPS pictures (21 of each emotion category, chosen using normative ratings). Pictures were displayed for 6 seconds with an ITI of 17 seconds. Startle probes (50 ms blasts of 95 decibel white noise) were presented through headphones at 4.5, 7, or 8 seconds into the trial (18 trials each) or not at all (9 trials). Corrugator EMG and blink (orbicularis) EMG were recorded with mini-electrodes throughout picture viewing (encoding). Participants were not informed that there would be a memory test later. REFERENCES Abercrombie, H. C., Speck, N. S., & Monticelli, R. M. (2006). Endogenous cortisol elevations are related to memory facilitation only in individuals who are emotionally aroused. Psychoneuroendocrinology, 31(2), 187-196. Bradley, M. M., Greenwald, M. K., Petry, M. C., & Lang, P. J. (1992). Remembering pictures: pleasure and arousal in memory. Journal of experimental psychology: Learning, memory, and cognition, 18(2), 379-390. Bradley, M. M., Codispoti, M., Cuthbert, B. N., & Lang, P. J. (2001). Emotion and motivation I: defensive and appetitive reactions in picture processing. Emotion, 1(3), 276-298. Davis, M. (1986). Pharmacological and anatomical analysis of fear conditioning using the fear-potentiated startle paradigm. Behavioral Neuroscience, 100(6), 814-824. Jackson, D. C., Malmstadt, J. R., Larson, C. L., & Davidson, R. J. (2000). Suppression and enhancement of emotional responses to unpleasant pictures. Psychophysiology, 37(4), 515-522. LeDoux, J. E. (1992). Brain mechanisms of emotion and emotional learning. Current Opinions in Neurobiology, 2(2), 191-197. Tassinary, L. G., & Cacioppo, J. T. (2000). The skeletomotor system: Surface electromyography. In J. T. Cacioppo, L. G. Tassinary & G. G. Berntson (Eds.), Handbook of Psychophysiology (2nd ed.). New York, NY: Cambridge University Press. For corrugator, there was an interaction between valence and memory (F(2,86)=4.075, p=0.020). Unpleasant pictures that were later remembered elicited MORE corrugator response than forgotten unpleasant pictures. Pleasant pictures that were later remembered elicited LESS corrugator response than forgotten pleasant pictures. ACKNOWLEDGEMENTS This work was made possible in part by institutional start-up funds to Heather Abercrombie (University of Wisconsin), and NIMH Institutional training grant number T32MH018931 from the National Institute of Mental Health (the Emotion Research Training Grant, which supports Michelle Wirth.) We are grateful to Nicole Speck, Natasha Shallow, Ashley Lienhardt, and Marie Kay for assistance with data collection. We also would like to thank Richard Davidson and Ned Kalin for advice and support. These effects were also found for recognition memory, in an overlapping but distinct sample (N=19).