Neural Signatures of Intransitive Preferences

It is often assumed that decisions are made by rank-ordering and thus comparing the available choice options based on their subjective values. Rank-ordering requires that the alternatives’ subjective values are mentally represented at least on an ordinal scale. Because one alternative cannot be at the same time better and worse than another alternative, choices should satisfy transitivity (if alternative A is preferred over B, and B is preferred over C, A should be preferred over C). Yet, individuals often demonstrate striking violations of transitivity (preferring C over A). We used functional magnetic resonance imaging to study the neural correlates of intransitive choices between gambles varying in magnitude and probability of financial gains. Behavioral intransitivities were common. They occurred because participants did not evaluate the gambles independently, but in comparison with the alternative gamble presented. Neural value signals in prefrontal and parietal cortex were not ordinal-scaled and transitive, but reflected fluctuations in the gambles’ local, pairing-dependent preference-ranks. Detailed behavioral analysis of gamble preferences showed that, depending on the difference in the offered gambles’ attributes, participants gave variable priority to magnitude or probability and thus shifted between preferring richer or safer gambles. The variable, context-dependent priority given to magnitude and probability was tracked by insula (magnitude) and posterior cingulate (probability). Their activation-balance may reflect the individual decision rules leading to intransitivities. Thus, the phenomenon of intransitivity is reflected in the organization of the neural systems involved in risky decision-making

Effects of healthy aging on hippocampal and rhinal memory functions: an event-related fMRI study

Event-related functional magnetic resonance imaging was used to study the effects of healthy aging on hippocampal and rhinal memory functions. Memory for past events can be based on retrieval accompanied by specific contextual details (recollection) or on the feeling that an event is old or new without the recovery of contextual details (familiarity). There is evidence that recollection is more dependent on hippocampus, whereas familiarity is more dependent on the rhinal cortex, and that healthy aging has greater effects on recollection than on familiarity. However, little evidence is available about the neural correlates of these effects. Here, we isolated activity associated with recollection and familiarity by distinguishing between linear and quasi-exponential ''perceived oldness'' functions derived from recognition confidence levels. The main finding was a double dissociation within the medial temporal lobes between recollection-related activity in hippocampus, which was reduced by aging, and familiarity-related activity in rhinal cortex, which was increased by aging. In addition, age dissociations were found within parietal and posterior midline regions. Finally, aging reduced functional connectivity within a hippocampal--retrosplenial/parietotemporal network but increased connectivity within a rhinal--frontal network. These findings indicate that older adults compensate for hippocampal deficits by relying more on rhinal cortex, possibly through a top--down frontal modulation. This finding has important clinical implications because early Alzheimer's disease impairs both hippocampus and rhinal cortex

The Hippocampus Is Coupled with the Default Network during Memory Retrieval but Not during Memory Encoding

The brain's default mode network (DMN) is activated during internally-oriented tasks and shows strong coherence in spontaneous rest activity. Despite a surge of recent interest, the functional role of the DMN remains poorly understood. Interestingly, the DMN activates during retrieval of past events but deactivates during encoding of novel events into memory. One hypothesis is that these opposing effects reflect a difference between attentional orienting towards internal events, such as retrieved memories, vs. external events, such as to-be-encoded stimuli. Another hypothesis is that hippocampal regions are coupled with the DMN during retrieval but decoupled from the DMN during encoding. The present fMRI study investigated these two hypotheses by combining a resting-state coherence analysis with a task that measured the encoding and retrieval of both internally-generated and externally-presented events. Results revealed that the main DMN regions were activated during retrieval but deactivated during encoding. Counter to the internal orienting hypothesis, this pattern was not modulated by whether memory events were internal or external. Consistent with the hippocampal coupling hypothesis, the hippocampus behaved like other DMN regions during retrieval but not during encoding. Taken together, our findings clarify the relationship between the DMN and the neural correlates of memory retrieval and encoding

Posterior midline and ventral parietal activity is associated with retrieval success and encoding failure

Contains fulltext : 123150.pdf (publisher's version ) (Open Access)The ventral part of lateral posterior parietal cortex (VPC) and the posterior midline region (PMR), including the posterior cingulate cortex and precuneus, tend to show deactivation during demanding cognitive tasks, and have been associated with the default mode of the brain. Interestingly, PMR and VPC activity has been associated with successful episodic retrieval but also with unsuccessful episodic encoding. However, the differential contributions of PMR and VPC to retrieval vs. encoding has never been demonstrated within-subjects and within the same experiment. Here, we directly tested the prediction that PMR and VPC activity should be associated with retrieval success but with encoding failure. Consistent with this prediction, we found across five different fMRI experiments that, during retrieval, activity in these regions is greater for hits than misses, whereas during encoding, it is greater for subsequent misses than hits. We also found that these regions overlap with the ones that show deactivations during conscious rest. Our findings further aid in clarifying the role of the default mode regions in learning and memory.10 p

Behavioral Results and fMRI Correlation Analysis

<div><p>Bars showing d-primes for scene encoding or target detection during concurrent recognition hits (R+) and misses (R–) for <i>Behavioral Experiment 1</i> (A), <i>fMRI Experiment</i> (B), and <i>Behavioral Experiment 2</i> (C).</p> <p>Note: * <i>p</i>-value < 0.05 and ** <i>p</i>-value < 0.005, and the error bars represent SEM.</p> <p>(D) Scatterplot showing the correlation between activity in left mid-VLPFC and the encoding suppression in the visual cortex/MTL. Each point represents the data from a single participant.</p></div

fMRI Results

<div><p>For the purpose of illustration, all activations are shown at <i>p</i> < 0.005.</p> <p>(A) Interaction between stage (E/R) and outcome (+/-) in PCC, E– = (R–E– and R+E–), E+ = (R–E+ and R+E+), R– = (R–E– and R–E+), R+ = (R+E– and R+E+).</p> <p>(B) A thre-step analysis indicated encoding suppression in the visual cortex and medial temporal lobe during concurrent retrieval. In step 1, a “localizer” task identified regions related to scene processing. In step 2, we defined encoding success areas within the remaining regions using the contrast R–E+ > R–E–. In step 3, we tested whether the mean encoding success activity of the remaining regions was reduced when successful retrieval happened concurrently.</p> <p>(C) Greater activity in left mid-VLPFC during concurrent, as compared to separate, successful encoding and retrieval (R+E+ > R+E– and R–E+). Bar graphs indicate the mean of all activated voxels (<i>p</i> < 0.001, uncorrected).</p></div

Main effects and interactions during episodic retrieval.

<p>Main effects and interactions during episodic retrieval.</p

Word Retrieval/Scene Encoding Task

<div><p>The experimental task involved three phases: <i>word encoding</i>, <i>word retrieval/scene encoding</i>, and <i>scene retrieval</i>.</p> <p>(A) During <i>word encoding</i>, participants studied words while making semantic (living/nonliving) decisions about the study items.</p> <p>(B) During <i>word retrieval/scene encoding</i>, participants performed an old/new word recognition task including words presented at <i>word encoding</i> as well as words that were not seen at study. Simultaneously, spatial scenes were presented in the background</p> <p>(C) During <i>scene retrieval</i>, encoding of these spatial scenes was tested during a picture recognition task.</p></div

Visual Attention Task

<p>The task involved two phases: a <i>word encoding phase</i> and a <i>word retrieval/visual attention phase</i>. During the <i>word encoding phase</i> (A), participants studied words while making semantic (living/nonliving) decisions about the study items. During <i>word retrieval/visual attention phase</i> (B), participants performed an old/new word recognition task including old words presented at word encoding as well as new words that were not seen at study. On half of the trials, a small dot was flashed in the background during word recognition. After every recognition response, a second response was required to indicate visual detection of the target dot.</p

Experimental Task.

<p>Encoding trials consisted of three periods: a 1-second cue period, a 3-second encoding period, and a 1.5-second rating period. During the cue period, participants were introduced with a cue word together with an icon that indicated the trial condition. During the encoding phase, dependent on the icon, they either imagined an image or sound associated with the word (internally oriented conditions: Int-Enc) or they either perceived a sound or image associated with the word (externally oriented conditions: Ext-Enc). During the rating period, participants rated the imagery quality or perceptual richness of their experience. Retrieval trials, presented on the subsequent day, consisted of two periods, a 4-sec retrieval period, and a 1.5-sec confidence rating period. During the retrieval period, participants viewed the cue words from the previous day and retrieved the correct encoding source (1 = imagined sound, 2 = heard sound, 3 = imagined image, 4 = observed image). During the confidence rating period, they rated their confidence about their retrieval decision (“unsure”/“sure”).</p