Memory Inhibition

In human memory system, the situations when some factor causes performance on a memory task to fall below some neutral baseline or control condition has been termed inhibition.

When a factor creates an improvement in performance relative to the control condition, the corresponding term is facilitation.

Many researchers refer to a process of inhibition that impairs responding (behavioral inhibition) or that keeps unwanted memories from clogging the mind when some desired information is sought (cognitive inhibition).

Interestingly, some researchers have argued that inhibition is critical for successful performance in many memory tasks; for example, if in looking for a parked car, one were forced to retrieve simultaneously all prior places in which one had parked.

At first blush, the idea of a process that impairs memory might seem off, because forgetting Opens in new window is considered undesirable by most people. More often than people realize, however, having good memory for a prior experience is not what we always want.

We are frequently confronted with intrusive reminding that undermine performance on some task or that otherwise distract us. Sometimes, these reminding are unpleasant—memories of trauma or loss, or of events that make us sad, anxious or embarrassed.

Other times, our motives for controlling unwanted memories may be utilitarian, as when we simply need to ensure that only the most current knowledge is accessed (e.g. today’s parking spot, and not yesterday’s).

When unwanted memories intrude into mind, some means of reducing their accessibility becomes desirable. So, for instance, upon confronting a reminder to an unpleasant memory, one may engage inhibition to stop retrieval Opens in new window, preventing the reminder from eliciting the memory.

Can the mechanisms that stop reflexive responses be engaged to override retrieval?

To study this, psychologists put people in a situation in which they repeatedly confronted a reminder to a recently encoded memory, and asked them to attend to the reminder while willfully excluding the associated memory from consciousness. Afterwards, the subjects were asked to recall the memories that they had previously kept out of awareness.

Interestingly, the repeated presentations of reminders during the prior no-think phase not only failed to improve people’s later retention of the associated memory—as one might ordinarily expect reminders to do—it impaired performance compared with performance on baseline items that were learned initially, but for which no reminders were presented in the interim.

Thus, excluding an unwanted memory from awareness leads to a memory deficit for the avoided trace, and the properties of this deficit are consistent with inhibition (Anderson and Green, 2001). Recent findings confirm that the brain mechanisms underlying this type of memory inhibition are related to the ability to override reflexive responses.

Suppressing unwanted memories recruits the dorsolateral prefrontal cortex, a brain region associated with inhibiting prepotent responses; this suppression reduces activation in the hippocampus, a structure associated with declarative memory (Anderson et al. 2004). Importantly, the engagement of frontal cortex and the modulation of hippocampal activation predict the amount of memory impairment for suppressed items.

Whether the forgetting produced by suppression reflects the direct or indirect consequences of neuronal inhibition remains to be established, although the impairment is clearly related to modulation of brain activity at the systematic level. The capacity to inhibit unwanted memories may help people regulate consciousness of unpleasant or intrusive memories.

What might cognitive inhibition mean?

According to the Oxford English Dictionary, there are four senses of inhibition. Two relate to societal or legal prohibition. Interestingly, the other two relate separately to the physiological and psychological senses of the term, consistent with present claim that these two senses are distinct.

The defining elements of cognitive inhibition appear to be two—mental withholding and reduced performance. The latter is directly measurable as reduced response likelihood or lengthened response latency, given a suitable neutral baseline or control condition against which to make the comparison. However, the former is an inference from performance. Inhibition is not an outcome; it is a theory about the cause of that outcome.