PTSD
Memory is compartmentalized and manifested in many different memory systems and neurocircuitry in the brain and central nervous system. Loss and disruption of one memory system removes its contribution from experience. Squire and colleagues have classified memory into two categories, i.e. implicit (i.e. memory and learning that is reflexive, sensorimotor, perceptual, habit, and not in awareness) and explicit (i.e. memory and learning that is intentional, volitional, and in awareness). Implicit memory is characterized by cortico-subcortical interactions and enhanced by medial temporal lobule contributions. Explicit memory is not only characterized by cortico-subcortical interactions, but also needs mediation by medial temporal lobe structures. Encoded memory is initially processed by the medial temporal lobe structures and is later consolidated and encrypted into different brain regions and neurocircuitry to allow for its later storage, recognition, or retrieval. Loss and disruption in consolidation processes also results in memory processing deficits such as recognition and retrieval.
Fear conditioning in animal fear conditioning paradigms can be likened to the human experience of perceived traumatic stress. In response to functional deficits in a post-training hippocampal formation (i.e. medial temporal lobe structures like the hippocampus, perirhinal and parahippocampal cortices), fear and aversive conditioning learning is delayed but intact and characterized by deficits in identifying fear-producing contexts. Fear conditioning is characterized by implicit learning and memory processes, but is enhanced by medial temporal lobe’s explicit memory processes. Posttraumatic stress disorder’s (PTSD) responses to traumatic stress are characterized by both implicit and explicit learning. It is fast learning like explicit learning, as one traumatic event is sufficient to elicit a traumatic response. It is also characterized by implicit learning’s difficulty in intentional explicit traumatic memory retrieval, is characterized by unintentional disturbing traumatic sensory intrusions (e.g. abreactions) and traumatic identification, unintentional reliving of trauma related affect reminiscent of the trauma, etc. According to neuroimaging findings PTSD regional activations are reminiscent of fear conditioning’s regional activations during mid-consolidation processes.
Talking therapies that focus on traumatic processing and retrieval help to reinstate traumatic narrative development and, explicit learning about the traumatic memory. They also help to reduce PTSD symptom expression and arousal. This process is mediated by retrieval processes that focus on traumatic personal meaningfulness. This is achieved by working with medial temporal lobe consolidation processes and reinstating the functional integrity of the medial prefrontal cortex (i.e. the perigenual anterior cingulate and medial orbitofrontal cortices). The medial prefrontal cortex is associated with proper sequencing, self-referential activity, self-identity, and personal meaningful emotion and cognition. According to neuroimaging findings the medial prefrontal cortex’s contribution is evident as trauma survivors own and remember traumatic memory.
Processes outlined above are not only critical for our understanding of consolidation processes and memory, but also can be useful in the planning and developing of neuropsychotherapy methods to treat psychiatric illness and other impairment.