The effect of midazolam on visual search: Implications for understanding amnesia

Abstract

The notion of multiple memory systems based on conscious accessibility has been supported largely by neuropsychological patient studies. Specifically, it was widely held that amnesic patients have impaired explicit memory performance but spared implicit memory performance. However, recent patient studies have called the implicit͞explicit memory distinction into question. In this study, normal participants were tested on a visual search task, once after an injection of midazolam, an anesthetic that induces temporary amnesia, and once after an injection of saline. Under the influence of midazolam, participants did not show facilitation in search times for repeated configurations (contextual cuing), although there was a general speed-up in performance across blocks in both the midazolam and saline conditions. Neither the contextual-cuing effect nor the procedural-learning effect was available to subjective experience, yet only one of these was affected by midazolam-induced amnesia. These data call into question the notion that memory systems divide on the basis of subjective experience of consciousness or reportability. Rather, the findings support the contention that anterograde amnesia affects learning that depends on building novel associations in memory and that this deficit does not hinge upon accessibility to consciousness. explicit memory ͉ implicit memory ͉ synthetic amnesia

Disruption of Sequential Priming in Organic and Pharmacological Amnesia: A Role for the Medial Temporal Lobes in Implicit Contextual Learning

“…We conclude that the critical medial temporal lobe structures related to amnesia serve the function of binding information together, regardless of whether that information is retrieved explicitly (declaratively) or implicitly (procedurally). Hence, as with other illustrations of impaired contextual learning in amnesia (Chun and Phelps, 1999;Park et al, 2004;Ryan et al, 2000), our findings do not support the idea that the hippocampus and medial temporal lobes control declarative memory alone.…”

Procedural learning and associative memory mechanisms contribute to contextual cueing: Evidence from fMRI and eye-tracking

“…Part of the evidence for hippocampal involvement was based on patients with damage to the HPC area that showed no advantage for repeated displays but still a strong improvement in performance with practice (Chun and Phelps 1999). This pattern was replicated with the drug midazolam that mimicked the results found with patients suffering from anterograde amnesia (Park et al 2004). Additional evidence for hippocampal involvement came from the fMRI study that showed that faster search times for repeated configurations corresponded to greater activation in HPC (Greene et al 2007).…”

“…There has been some debate concerning the nature of the mechanism involved in the contextual cueing effect in terms of the brain regions engaged in the facilitation of search for repeated displays (Chun and Phelps 1999;Manns and Squire 2001;Park et al 2004;Greene et al 2007;Preston and Gabrieli 2008). Some researchers have argued that contextual cueing relies on hippocampus (Chun and Phelps 1999;Greene et al 2007), the region critical for associative memory.…”

Experience-Dependent Eye Movements, Awareness, and Hippocampus-Dependent Memory

“…Thus, it appears that damage beyond the hippocampus is needed to impair perceptual learning in this task, and the available data do not contradict the idea that hippocampus-dependent memory is accessible to conscious recollection. Another study using the same task found that midazolam affected perceptual learning, particularly the learning of repeated displays (Park et al, 2004). However, the effects of midazolam are not limited to the hippocampus (Taguchi et al, 1989;Veselis et al, 1997), and they also extend to hippocampusindependent cognitive functions (Polster et al, 1993;Hirshman et al, 1999;Fisher et al, 2006).…”