Are there any experiments in humans where despite episodic-memory amnesia they still preserve (associative) fear conditioning developed during the episode/event that is lost from episodic memory?

I'm hoping maybe it was tested in someone like Henry Molaison whether someone could develop fear conditioning but not remember how they've got it, i.e. a form of source amnesia but for [fear] conditioning rather than the usual notion of source amnesia for some [declarative memory] knowledge.

Wikipedia does mention that:

Experiments involving repetition priming underscored Molaison's ability to acquire implicit (non-conscious) memories, in contrast to his inability to acquire new explicit semantic and episodic memories (Corkin, 2002).

However, looking myself at that paper, it seems all experiments (mentioned there) were done with semantic priming rather any form of affective priming.

  • 1
    $\begingroup$ This a sort of generalization of what someone asked here recently about a narrower line of events: psychology.stackexchange.com/questions/18847/… but I'm interested in controlled experimental evidence rather than providing post-hoc explanations for someone's life experience(s). $\endgroup$ – Fizz Jan 9 '18 at 3:42
  • 1
    $\begingroup$ Also, I don't want to get here into a discussion whether fear conditioning is (or isn't) a good model of anxiety disorders... I'm somewhat aware of those issues. Fear conditioning is easy to test experimentally though, which is why my question is about it, although the amnesia part of my questions surely is not easy to set up (ethically anyway). $\endgroup$ – Fizz Jan 9 '18 at 4:52
  • 2
    $\begingroup$ Fear conditioning is produced from amygdala, a very primitive brain component, also know as the "Lizard brain", so I would expect it to function very well even for amnesiacs. But I do not know any studies that tested it. $\endgroup$ – DesignerAnalyst Jan 9 '18 at 6:01
  • 1
    $\begingroup$ @DesignerAnalyst: I'm not sure that's enough though. Is the association (with the conditioned stimulus) also stored in the amygdala? If causal experimental evidence is lacking, I'll surely consider (i.e. upvote :0) neuroimaging correlates towards a (tentative) answer. $\endgroup$ – Fizz Jan 9 '18 at 6:46

As a sort of partial answer, but since it's too much to add to the question itself... a more encompassing question would be whether fear conditioning can occur without awareness of the conditioning event happening at all. I suppose an affirmative answer to the latter implies the answer is also "yes" to my question because forgetting the association event doesn't seem any more restrictive than not learning (into episodic memory) about it in the first place.

However, the jury seems to still be out on whether unaware conditioning can happen in humans. Some initial (and highly cited) studies answered the question affirmatively, but later studies cast doubt on the results because the level of awareness for the stimuli used seem to vary with the individual. (In other words, there was heterogeneity in awereness in the original studies; for a completely different reason, I've looked into what happens in such a case and asked what the phenomenon is called on cross-validated, but with not very satisfying answers insofar) From a 2005 review by Pessoa, which summarized the research up to then:

Does the processing of emotional stimuli depend upon awareness? Two influential neuroimaging papers, both of which appeared in 1998, reported that responses in the human amygdala occur in the absence of visual awareness. Awareness was manipulated by employing backward masking, as introduced by Esteves and Ohman in a behavioural paradigm. In one study, fearful faces were shown for 33 ms and were immediately replaced by a neutral ‘mask’ face that was presented for 167 ms. Subjects were naive as to the stimulus conditions, which included masked fearful and masked happy faces. Stronger responses were observed in response to fearful rather than happy faces (both masked by neutral faces), even though, upon subsequent debriefing, subjects did not report seeing any emotional faces. In another study, Morris et al. combined backward masking with classical conditioning to investigate responses to perceived and non-perceived angry faces. Although the participants did not report seeing the masked angry stimuli (angry faces were shown for 30 ms and followed by a neutral mask that was shown for 45 ms), the contrast of conditioned and non-conditioned masked angry faces activated the right amygdala. Recent studies have also gathered evidence for unaware processing by the amygdala For instance, Glascher and Adolphs showed that in normal controls, but not in patients with amygdala lesions, arousal ratings correlated with skin conductance responses for both subliminal (unaware) and supraliminal (aware) conditions (see Glossary). Together with the important earlier work by Ohman and colleagues, these results have strengthened the view that emotional processing occurs independently of conscious awareness. In general, a stimulus that is shown for about 30 ms before masking is considered to be at the ‘threshold’ for awareness.

However, a recent study by Phillips et al. did not observe any response in the amygdala during unaware conditions. The authors compared aware conditions, in which target faces (fearful or disgusted) were shown for 170 ms and followed by a mask that was shown for 100 ms, with unaware conditions, in which target faces were shown for 30 ms and, again, followed by a mask that was shown for 100 ms. Unlike prior studies, however, no differential responses were observed in the amygdala in association with fearful faces in the unaware condition (or in the anterior insula for unaware disgusted faces).

A crucial issue in the assessment of awareness is the criteria used to determine whether a participant is aware or unaware of a stimulus. According to ‘objective’ criteria, unaware perception occurs when a subject’s performance in a ‘forced-choice’ task is at chance. Under such conditions, behavioral effects of unaware stimuli (e.g. faster reaction time to undetected fearful faces), as well as the associated fMRI signals, constitute correlates of unaware perception. According to ‘subjective’ criteria, unaware perception occurs when subjects report that they are unable to perform the task better than by chance (independent of their actual objective performance). Although some of the previous studies used forced-choice objective methods, they did not assess performance in a manner that is independent of response bias on an individual-by-individual basis [...]. This is important because in the face of weak, noisy signals, subjects might indicate that they do not detect target stimuli and thus appear to be unable to detect them reliably. A recent behavioral study by Pessoa et al. addressed these issues by analyzing performance by way of signal detection methods. The authors varied the duration (17, 33 and 83 ms) of which a target face (fearful, happy or neutral) was shown before being immediately replaced by a neutral-face mask (which was shown for 116, 100, and 50 ms, respectively, such that the target plus mask lasted 133 ms in each case). The subject’s task was to report explicitly whether or not a fearful face was presented in each trial, and also to rate their confidence in this decision. Although some subjects only reliably detected the fearful targets that were shown for 83 ms, 36% of the participants were able to detect both the 33 ms and 83 ms targets. Remarkably, some subjects could even detect fearful faces that were shown for 17 ms before masking. These results demonstrated that participants differ widely in their sensitivity to fearful faces (Figure 1). Moreover, the results revealed that even very brief (17 ms) stimuli can be incompletely masked, consistent with another recent study [Maxwell and Davidson]. The findings by Pessoa et al. also raise the possibility that the discrepancy between the results of Phillips et al. nd those of prior studies might be caused, at least in part, by variability in sensitivity among individuals, which may be related to anxiety levels.

enter image description here

I'm not sure if there's a more recent review than this perhaps with different conclusions following newer experiments. The fact that the review was written by someone who also contributed primary research in the "cast doubt" direction casts a little doubt (in my mind) on its objectivity... But the above surely illustrates the difficulty in conducting studies related to awareness.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.