#10624 - Episodic Future Thinking - Neuropsychology of Memory

Episodic Future Thinking (1)

The Mental Time Travel (MTT) Hypothesis (Suddendorf & Corballis, 2007)

• Comprises the mental reconstruction of personal events from the past (EM) + the mental construction of possible events in the future

• Those events are experiences as if they were occurring now

• Ability depends on the sophistication of other cognitive capacities - self-awareness, meta-representation , mental attribution + the ability to dissociate imagined mental states from one’s own present mental state

• These abilities are also important aspects of ToM

• In view of the generative aspect of EM - seems reasonable to suppose that basically the same mechanisms might be involved in imaging the future as in constructing the past

• Time travel into the future is in a sense an extrapolation from time travel in the past - similarly involving the ability to escape the influence of the current mental state

• Thinking about one’s personal future (episodic future thinking) may be the real driver behind episodic memory

What might episodic memory and imaging the personal future have in common?

• Retrieval of relevant information

• Personal perspective

• Sense of presence /self (autonoetic consciousness)

• Narrative structure?

• Imagery?

• Spatial + contextual structure/detail ?

If MTT is a single cognitive process:

1. Patients with impairments travelling back in time (amnesia) should also show impairments projecting forwards in tie

2. Traveling backwards + forwards in time should show overlapping patterns of brain activation in intact participants

Do amnesic patients have problems with imaging future events ?

• Buckner & Carroll (2006)

• Makes reference to an excerpt of conversation between Tulving and amnesic patient KC

• Asked “What will you be doing tomorrow?” – says he doesn’t know + describes his state of mind when thinking about tomorrow as “blank”

• Steinvorth & Corkin

• HM - does not make predictions about future autobiographical events - when pushed to make a prediction - either responded with an event from the distant past or doesn’t respond at all

Not all future thinking is impaired:

• Only those involving a personal perspective - future projections involving the self – sense of presence/self

• Non-personal future events Klein, Loftus & Kihlstrom (2002) – patient DB

• Severely amnesic following anoxic episode

• Could not coherently answer questions about his personal future BUT retained semantic knowledge of the future – asked to talk about an issue which faced the environment – said weather rainfall patterns would change due to industrial pollution

• Lacks the ability to consider his personal past + future but can reason about a non-personal semantic future

Do all people with impaired episodic memory have impaired future thinking

Addis et al (2009)

• Tested the ability of 16 Alzheimer’s patients (mild – early stages) and 16 age matched controls to generate past + future autobiographical events using an adapted version of the Autobiograpical interview

• Event transcriptions were segmented into distinct details classified as either internal (episodic) or external (non-episodic)

• AD patients exhibited deficits in both remembering past events + stimulating future events - generating fewer internal + external episodic details than health older controls

• Patients were much worse at producing internal details of events for both past + future compared to controls

• The internal + external detail scores were strongly correlated across past + future events - providing further evidence of the close linkages between the mental representations of past and future.

Hassabis et al (2007)

• Tested whether a group of amnesic patients with primary damage bilateraly to the hippocampus could construct new imagined experiences in response to short verbal cues - outline common place scenarios – v IQ + aged matched controls

• Cue => “imagine you are lying on a white sandy beach in a beautiful tropical bay”

• Participant instructed to vividly imagine the situation from the cue + describe it in as much (multimodal) detail as possible - explicitly told not to recount an actual memory

• Content of descriptions divided into four categories :spatial reference, entity presence, sensory description + thought/emotion/action

• RESULTS

• Patient sig impaired on the task systematic study formally documents hippocampal amnesic patients difficulty in richly imagining new experiences

• Findings offer some insight into the mechanism which could underpin the deficits patients imagined experiences were strikingly deficient in spatial coherence - resulting in their constructions being fragmented + lacking richness

• Suggested that the hippo makes a critical contribution to the creation of new experiences providing the spatial context of the environmental setting into which the details are bound the absence of this function mediated by the hippo - fundamentally affects the ability to re-experience or reconstruct past events

• According to the traditional view of memory - role of the hippo in EM is time-limited, with these memories consolidated to the neocortex over time

• Within this framework it is held that the neocortex contains generalised representation for spatial contextual + non spatial memories - supports memory independently of any contribution from the hipp/MTL

• According to this view - successful imagination of experiences would be expected to occur in the presence of hippo lesions - as the co-ordination of activity in multiple neocortical areas

• Demonstration that patients with hippo lesions are impaired at generating new imagined exp’s poses a challenge to the traditional model

• However it could be argued that the creation of imagined exp’s relies on the retrieval of recent episodic memories - process severely disrupted in hippo amnesics ? – seems unlikely

Neuroimaging

Botzung et al (2008):

• fMRI used in healthy subjects to investigate the existence of common neural structures supporting re-experiencing the past + pre-experiencing the future

• presented with cue cards - try to generate a memory - either related to a prev generated memory of a future plan

• Asked to mentally re-experience their recollections OR pre-experience their future projections

• Past and future event evocation appears to involve highly similar patterns of activation

• Medial prefrontal cortex , posterior regions + the MTL

• Frontal activations are likely to be related to decision making

• Posterior activations are likely to be visual activations relating to imagery

• MTL activations may related to MTT

• Results seem to support the view of a common neurocognitive system - which would allow humans to mentally travel through time - idea that re-experiencing + pre-experiencing past + future events may rely on similar cognitive capacities

Evidence from Developmental Amnesia Maguire et al (2010)

• One patient PO1 – found to be unimpaired on tasks requiring imagination of fictitious + future experiences – despite dense amnesia + 50% volume loss in both hippocampi

• Compared this to “Jon” – patient with similar neuropsychological profile - developmental amnesia + 50% reduction in hippo volume bilaterally

• Compared to 5 patients with amnesia - primary damage to hippo bilaterally - acquired in adulthood + 10 healthy control ptp’s

• Cue scenario – same as Habbassis et al (2007) imagine on sandy beach - vividly imagine + give as much detail as pos

• Spatial coherence index = indicate statements which accurately describe the constructions of their scenes - mainly integrated or fragmented?> experiential index = from 0-60 measures overall richness of the imagined experience

• RESULTS

• Patient group scored sig lower of the experierential index than control group - also much lower spatial coherence index

• However patient P01 was not impaired at the task

• Also no sig difference between on + controls on the experiential index - simalryl performed close to controls of spatial coherence

• John’s preserved scene construction ability shows that PO1 was not an isolated atypical case some confluence of factors can arise that leads to preserved scene construction in the context of hippo amnesia

• Authors suggest that the activity of their residual hippocampal tissue supports the ability to imagine new scenarios - that this is the key feature

• Residual hippo tissue was active in both patients + in similar circumstances to control ptp’s during autobio memory retrieval + semantic learning in P01 -- cannot def relate function to these hippo activations – activations are suggestive of preserved hippo function – may aid their preserved ability to imagine future scenarios (Hassabis et al, 2010)

• Further research is needed – fMRI with patients whose scene construction abilities are intact - see which brain regions are engaged

Mullaly et al (2014) amnesics also problems in imagining hypothetical events

• Examined scene construction during fMRI in Jon - well characterised patient with DA - preserved scene construction + 21 amnesic control ptps from Hassabis et al 2007

• Ptp’s presented with a trial cue – hypothetic events “imagine standing on crowded train platform” - then screen = close eyes + imagine - 16s visualisation period - focus on scene

• Amnesics also impaired at imaging hypothetical future events – these two things engage the same brain regions - particularly the R hippo

• When Jon engaged in scene construction - he activated many of the regions known to be associated with imagining scenes + imaging future events in controls - VMPFC, posterior cingulate however – activity was not increased in the hippocampal tissue

• Direct comparisons with a...