The role of the hippocampus in the retrieval of a spatial location

Based on computational models of the hippocampus, it has been suggested that a possible mechanism for memory retrieval is pattern completion, wherein an autoassociative network recalls previous patterns of activity given noisy or degraded cues. However, there are few behavioral data examining pattern completion per se in the hippocampus. Here, we present a study in which rats were tested on a spatial location retrieval paradigm, each trial of which consisted of a sample and choice phase. During the sample phase, rats were trained to displace an object in one of 15 possible locations to retrieve a food reward and return to the start-box on a cheeseboard maze. The object was then removed and the same location was re-baited for the choice phase. The rats' accuracy in returning to the correct location was recorded. On test trials, visual extramaze cues, vestibular cues, or both were manipulated to assess pattern completion in normal rats. Subjects were then randomly assigned to receive a cortical control, a sham, or a dorsal and ventral hippocampal lesion and were retested on the task. Control and unoperated rats were able to perform the task when visual extramaze or vestibular cues were reliable, but not when they were manipulated. Rats with hippocampal lesions were impaired in the baseline condition, as well as during all manipulations. These results support the hypothesis that the hippocampus supports the retrieval of a spatial location, possibly through a process of pattern completion.     

Integrating cognitive function screening and assessment into the routine care of multiple sclerosis patients

Cognitive dysfunction, a common feature of multiple sclerosis (MS), frequently leads to impaired activities of daily living, social skills deficits, diminished social support, and unemployment. There is growing evidence indicating that cognitive impairment is amenable to the effects of medication and behavioral counseling. Unfortunately, routine neuropsychological testing is rare in MS clinics because screening is ineffective and testing strategies are often too cumbersome or expensive. Recent research supports the reliability of a brief screening test called the Multiple Sclerosis Neuropsychological Screening Questionnaire as well as a minimal neuropsychological battery called the Minimal Assessment of Cognitive Function in Multiple Sclerosis. Data indicate that the Multiple Sclerosis Neuropsychological Screening Questionnaire has excellent split-half and test-retest reliability, and that it predicts neuropsychological deficiency with good sensitivity and specificity. Recently acquired data also show that the Minimal Assessment of Cognitive Function in Multiple Sclerosis tests have good test-retest reliability, discriminate MS patients from normal controls, and predict unemployment in MS patients. Thus, these or similar methods should be employed for the routine monitoring of cognitive functioning of MS patients.     

Retrieving text inferences: Controlled and automatic influences

Bridging inferences contribute to text coherence by identifying the connections among ideas, whereas elaborative inferences simply specify sensible extrapolations from text. Bridging inferences have been indistinguishable from explicit text ideas on numerous measures, suggesting similar longterm memory (LTM) representations for the two, whereas elaborative inferences are inferior. To evaluate the LTM representations of text ideas, we used the extended process-dissociation procedure (Buchner, Erdfelder, & Vaterrodt-Plunnecke, 1995; Jacoby, 1991) to partition the controlled, recollective contributions to text retrieval from the automatic, familiarity-based contributions. The automatic contribution to the recognition of implied concepts was consistently negligible, an outcome consistent with the absence of perceptual processing of those concepts during the original reading. In addition, the controlled basis of recognition was consistently higher for explicit than for implicit concepts, which suggests a more robust conceptual representation for explicit text ideas (Yonelinas, 2002). These results were interpreted to reflect the asymmetric representation of explicit ideas and inferences (elaborative and even bridging inferences) in the surface, propositional textbase, and situational levels of text representation.     

Contextualism and the Skeptic: Comments on Engel

Mylan Engels paper (2004) is divided into two parts: a negative part, criticizing the costs of contextualism and a constructive part proposing a noncontextualist resolution of the skeptical problem. I will only address the constructive part here. The constructive part is composed of three elements: (i) a reconstruction or reformulation of the original skeptical argument, which draws on the notion of epistemic possibility (e-possibility), (ii) a distinction between two senses of knowledge (and two corresponding kinds of e-possibility): fallibilistic and infallibilistic, and (iii) an argument which tries to hoist the skeptic by their own petard, namely the closure principle (CP). As I will argue, there are two ways to understand Engels anti-skeptical argument. Only in one interpretation does the argument depend on the proposed reconstruction of the skeptical argument in terms of e-possibility. But this version of the argument is unsound. More importantly, the skeptic has a strong prima facie objection at her disposal, which applies to both interpretations of the argument. If this objection is valid, Engels argument does not hold. But once it is invalidated, his argument is superfluous.     

When does word meaning affect immediate serial recall in semantic dementia?

Patients with semantic dementia can show superior immediate recall of words that they still understand relatively well, as compared with more semantically degraded words, suggesting that conceptual knowledge makes a major contribution to phonological short-term memory. However, a number of studies have failed to show such a recall difference, challenging this view. We examined the effect of several methodological factors on the recall of known and degraded words in 4 patients with semantic dementia, in order to investigate possible reasons for this discrepancy. In general, our patients did exhibit poorer recall of the degraded words and made more phonological errors on these items. In addition, set size affected the magnitude of the recall advantage for known words. This finding suggests that semantic degradation influenced the rate of learning in the immediate recall task when the same items were presented repeatedly. The methods used to select known and degraded items also impacted on the recall difference. List length, however, did not affect the advantage for known words. The coherence of items in phonological short-term memory was affected by their semantic status, but not by the length of the material to be retained. The implications of these findings for the role of semantic and phonological representations in verbal short-term memory are discussed.     

Temporal coding in conditioned inhibition: analysis of associative structure of inhibition

Two experiments with rats as subjects were conducted to investigate the associative structure of temporal control of conditioned inhibition through posttraining manipulation of the training excitor-unconditioned stimulus (US) temporal relationship. Experiment 1 found that following simultaneous Pavlovian inhibition training (i.e., A --> US/XA-no US) in which a conditioned stimulus (CS A) was established as a delay excitor, maximal inhibition was observed on a summation test when CS X was compounded with a delay transfer CS. Furthermore, posttraining shifts in the A-US temporal relationship from delay to trace resulted in maximal inhibition of a trace transfer CS. Experiment 2 found complementary results to Experiment 1 with an A-US posttraining shift from serial to simultaneous. These results suggest that temporal control of inhibition is mediated by the training excitor-US temporal relationship.     

Trial spacing is a determinant of cue interaction

Four conditioned lick suppression experiments with rats examined the effect of trial spacing on cue interaction. Experiments 1 and 2 found overshadowing to be eliminated with massed compound stimulus-outcome pairings and the usual trial spacing effect to be reversed with compound acquisition trials. Experiment 3 found that whether acquisition compound-outcome pairings were massed or spaced determined the effect of posttraining extinction treatment. Extinction of the overshadowing cue reduced responding following massed training and increased responding following spaced training. Extinction of the context decreased responding following massed training. Experiment 4 found the conditioning and devaluation results to be associative and stimulus specific. These results are in accord with the extended comparator hypothesis (J. C. Denniston, H. I. Savastano, & R. R. Miller, 2001).     

Location, location, location: the misprediction of satisfaction in housing lotteries

People tend to overestimate the emotional consequences of future life events, exhibiting an impact bias. The authors replicated the impact bias in a real-life context in which undergraduates were randomly assigned to dormitories (or "houses"). Participants appeared to focus on the wrong factors when imagining their future happiness in the houses. They placed far greater weight on highly variable physical features than on less variable social features in predicting their future happiness in each house, despite accurately recognizing that social features were more important than physical features when asked explicitly about the determinants of happiness. In Experiment 2, we found that this discrepancy emerged in part because participants exhibited an isolation effect, focusing too much on factors that distinguished between houses and not enough on factors that varied only slightly, such as social features.     

Dissociable neural systems for recognizing emotions

This study tested the hypothesis that the recognition of emotions would draw upon anatomically separable brain regions, depending on whether the stimuli were static or explicitly conveyed information regarding actions. We investigated the hypothesis in a rare subject with extensive bilateral brain lesions, patient B., by administering tasks that assessed recognition and naming of emotions from visual and verbal stimuli, some of which depicted actions and some of which did not. B. could not recognize any primary emotion other than happiness, when emotions were shown as static images or given as single verbal labels. By contrast, with the notable exception of disgust, he correctly recognized primary emotions from dynamic displays of facial expressions as well as from stories that described actions. Our findings are consistent with the idea that information about actions is processed in occipitoparietal and dorsal frontal cortices, all of which are intact in B.'s brain. Such information subsequently would be linked to knowledge about emotions that depends on structures mapping somatic states, many of which are also intact in B.'s brain. However, one of these somatosensory structures, the insula, is bilaterally damaged, perhaps accounting for B.'s uniformly impaired recognition of disgust (from both static and action stimuli). Other structures that are damaged in B.'s brain, including bilateral inferior and anterior temporal lobe and medial frontal cortices, appear to be critical for linking perception of static stimuli to recognition of emotions. Thus the retrieval of knowledge regarding emotions draws upon widely distributed and partly distinct sets of neural structures, depending on the attributes of the stimulus.