Why does stress make it hard to pull up the right memory?
One major route is through the brain's control systems. Traumatic stress is associated with altered function in the prefrontal cortex, a region important for executive functions such as attention, response inhibition, and cognitive control [3]. When these control processes are weakened, a person may struggle to suppress intrusive or irrelevant memories and to deliberately retrieve the memory they want. A review of forgetting mechanisms concluded that stress-induced disruption of memory recall operated specifically via executive and inhibitory functions [4].
This control-based explanation fits with studies of memory suppression. People differ in how well they can intentionally suppress unwanted memories, and this ability is linked to executive control and inhibitory mechanisms [2]. After analogue trauma, individual differences in retrieval suppression predict how many intrusive memories people later experience [1]. In other words, the failure is not necessarily that the memory was never stored, but that the retrieval system cannot keep unwanted memories out and bring the intended one in.
The hippocampus shows that recall is not only about control
Stress also affects the hippocampus, a brain structure critical for memory. In children with posttraumatic stress symptoms, one study found reduced activation of the right hippocampus during memory retrieval, even after controlling for IQ [3]. This suggests that the brain's memory retrieval machinery itself can be altered by traumatic stress, not just the prefrontal control systems that guide it.
That said, the same study frames these changes alongside effects on executive functions such as attention and response inhibition [3]. So the hippocampus finding does not rule out a control-based explanation; it may mean that stress affects both the control network and the memory structures it acts on.
When encoding and consolidation are part of the story
The idea that stress disrupts recall mainly through executive and inhibitory control is best supported for the specific phenomenon of stress-induced recall disruption in otherwise functioning memory systems [4]. But the same review also examined encoding impairments and consolidation problems in pathological forgetting, such as mild cognitive impairment [4]. In those conditions, the memory may never have been properly formed or stabilized, so the problem is not only retrieval control.
Similarly, traumatic stress in youth is linked to broad changes in brain development that can affect learning and memory more generally [3]. This means that in real-world traumatic stress, especially when it is early or severe, encoding and consolidation cannot be cleanly separated from control processes. The control-based account is a strong explanation for acute recall failures, but it is not the whole picture for all stress-related memory problems.
Sources used in this answer
Memory control ability modulates intrusive memories after analogue trauma
Individual differences in retrieval suppression, an inhibitory control process, predict intrusive memories after analogue trauma.
Heart rate variability predicts control over memory retrieval
Heart rate variability, a marker of executive control, is associated with individual differences in successfully suppressing unwanted memories.
Can traumatic stress alter the brain? Understanding the implications of early trauma on brain development and learning
Children with posttraumatic stress symptoms show reduced right hippocampal activation during memory retrieval and altered executive functions including attention and response inhibition.
Mechanisms of Forgetting: A Systematic Review of Neurocognitive and Clinical Determinants
A systematic review concludes that stress-induced disruption of memory recall operates specifically via executive and inhibitory functions, while pathological forgetting in mild cognitive impairment involves encoding and consolidation impairments.