Cue- versus probe-dependent prefrontal cortex activity during contextual remembering

Ian G. Dobbins and Sanghoon Han

Journal of Cognitive Neuroscience 18:1439-1452 (2006)

Functional neuroimaging comparisons of context and item memory frequently implicate the left prefrontal cortex (PFC) during the recovery of contextually specific memories. However, because cues and probes are often presented simultaneously, this activity could reflect operations involved in planning retrieval or instead reflect later operations dependent upon the memory probes themselves, such as evaluation of probe-evoked recollections. More importantly, planning related activity, wherein subjects reinstate details outlining the nature of desired remembrances, should occur in response to contextual memory cues even before retrieval probes are available. Using event-related functional magnetic resonance imaging, we tested this by dissociating cue- from probe-related activity during context memory for pictures. Cues forewarning contextual memory demands yielded more activity than those forewarning item memory in the left lateral precentral gyrus, midline superior frontal gyrus, and right frontopolar cortex. Thus, these anticipatory, cue-based activations indicated whether upcoming probe decisions would require contextually specific memories or not. In contrast, the left dorsolateral/midventrolateral and anterior ventrolateral PFC areas did not show differential activity until the probes were actually presented, demonstrating greater activity for context than for item memory probes. Direct comparison of proximal left PFC regions demonstrated qualitatively different response profiles across cue versus probe periods for lateral precentral versus dorsolateral regions. These results potentially isolate contextual memory-planning-related processes from subsequent processes such as the evaluation of recollections, which are necessarily dependent on individual probe features. They also demonstrate that contextual remembering recruits multiple, functionally distinct PFC processes.

Neural mechanisms mediating optimism bias

Tali Sharot, Alison M. Riccardi, Candace M. Raio, and Elizabeth A. Phelps

Nature 450:102-105 (2007)

Human expect positive events in the future even when there is no evidence to support such expectations. For example, people expect to live longer and be healthier than average, they underestimate their likelihood of getting a divorce, and overestimate their prospects for success on the job market. We examined how the brain generates this pervasive optimism bias. Here we report that this tendency was related specifically to enhanced activation in the amygdale and in the rostral anterior cingulate cortex when imagining positive future events relative to negative ones, suggesting a key role for areas involved in monitoring emotional salience in mediating the optimism bias. These are the same regions that show irregularities in depression, which has been related to pessimism. Across individuals, activity in the rostral anterior cingulate cortex was correlated with trait optimism. The current study highlights how the brain may generate the tendency to engage in the projection of positive future events, suggesting that the effective integration and regulation of emotional and autobiographical information supports the projection of positive future events in healthy individuals, and is related to optimism.

Neural events that underlie remembering something that never happened

Brian Gonsalves and Ken A. Paller

Nature Neuroscience 3:1316-1321 (2000)

We induced people to experience a false-memory illusion by first asking them to visualize common objects when cued with the corresponding word; on some trials, a photography of the object was presented 1800 ms after the cued word. We then tested their memory for the photographs. Posterior brain potentials in response to words at encoding were more positive if the corresponding object was later falsely remembered as a photography. Similar brain potentials during the memory test were more positive for true than for false memories. These results implicate visual imagery in the generation of false memories and provide neural correlates processing differences between true and false memories.

Augmenting mental chronometry: The P300 as a measure of stimulus evaluation time

Marta Kutas, Gregory McCarthy, and Emanuel Donchin

Science 197:792-795 (1977)

A technique for measuring the latency of the P300 component of event-related brain potentials on individual trials is described. Choice reaction times and the latency of P300 were compared under speed-maximizing and under accuracy-maximizing instructions. The choice stimuli required different levels of semantic categorization. The data support the proposition that the latency of P300 corresponds to stimulus evaluation time and is independent of response selection.

Source of dual-task interference: Evidence from human electrophysiology

Steven J. Luck

Psychological Science 9:223-227 (1998)

When an individual attempts to perform two tasks at the same time, the tasks often interfere with each other. This interference has been studied for several decades with the psychological refractory period paradigm, in which two targets that require independent responses are presented on each trial, separated by a variable delay period, interference typically takes the form of increased response times for the second target at short interstimulus delays. The present study used electrophysiological recordings to determine whether a specific index of perception and categorization (the P3 wave) is delayed in the same manner as response times. Although response times for the second target were found to be greatly delayed at short interstimulus interval, the P3 wave was not substantially delayed. This finding indicates that there was minimal interference during target identification and categorization and that the prolongation of response times in this paradigm primarily reflects a delay in a relatively late process such as response selection.

Time course of word identification and semantic integration in spoken language

Cyma Van Petten, Seana Coulson, Susan Rubin, Elena Plante, and Marjorie Parks

Journal of Experimental Psychology: Learning, Memory and Cognition 25:394-417 (1999)

The minimum duration signal necessary to identify a set of spoken words was established by the gating technique; most words could be identified before their acoustic offset. Gated words were used as congruent and incongruent sentence completions, and isolation points established in the gating experiment were compared with the time course of semantic integration evident in event-related brain potentials. Differential N400 responses to contextually appropriate and inappropriate words were observed about 200 ms before the isolation point. Semantic processing was evident before the acoustic signal was sufficient to identify the words uniquely. Results indicate that semantic integration can begin to operate with only partial, incomplete information about word identity. Influences of semantic constraint, word frequency, and rate of presentation are described.

Brain activity during speaking: From syntax to phonology in 40 milliseconds

Miranda van Turennout, Peter Hagoort, Colin M. Brown

Science 280:572-574 (1998)

In normal conversation, speakers translate thoughts into words at high speed. To enable this speed, the retrieval of distinct types of linguistic knowledge has to be orchestrated with millisecond precision. The nature of this orchestration is still largely unknown. This report presents dynamic measures of the real-time activation of two basic types of linguistic knowledge, syntax and phonology. Electrophysiological data demonstrate that during noun-phrase production speakers retrieve the syntactic gender of a noun before its abstract phonological properties. This two-step process operates at high speed: the data show that phonological information is already available 40 millisecond after syntactic properties have been retrieved.

A structural-functional basis for dyslexia in the cortex of Chinese readers

Wai Ting Siok, Zhendong Niu, Zhen Jin, Charles A. Perfetti and Li Hai Tan

PNAS 105:5561-5566 (2008)

Developmental dyslexia is a neurobiologically based disorder that affect ~5-17％ of school children and is characterized by a severe impairment in reading skill acquisition. For readers of alphabetic (e.g., English) language, recent neuroimaging studies have demonstrated that dyslexia is associated with weak reading-related activity in left temporoparietal and occipitotemporal regions, and this activity difference may reflect reductions in gray matter volume in these areas. Here, we find different structural and functional abnormalities in dyslexic readers of Chinese, a non-alphabetic language. Compared with normally developing controls, children with impaired reading in logographic Chinese exhibited reduced gray matter volume in a left middle frontal gyrus region previously shown to be important for Chinese reading and writing. Using functional MRI to study language-related activation of cortical regions in dyslexics, we found reduced activation in this same left middle frontal gyrus region in Chinese dyslexics versus controls, and there was a significant correlation between gray matter volume and activation in the language task in this same area. By contrast, Chinese dyslexics did not show functional or structural (i.e., volumetric gray matter) differences from normal subjects in the more posterior brain systems that have been shown to be abnormal in alphabetic-language dyslexics. The results suggest that the structural and functional basis for dyslexia varies between alphabetic and nonalphabetic languages.

A decrease in brain activation associated with driving when listening to someone speak

Marcel Adam Just, Timothy A. Keller and Jacquelyn Cynkar

Brain Research 1205:70-80 (2008)

Behavioral studies have shown that engaging in a secondary task, such as on talking on a cellular telephone, disrupts driving performance. This study used functional magnetic resonance imaging (fMRI) to investigate the impact of concurrent auditory language comprehension on the brain activity associated with a simulated driving task. Participants steered a vehicle along a curving virtual road, either undisturbed or while listening to spoken sentences that they judged as true or false. The dual-task condition produced a significant deterioration in driving accuracy caused by the processing of the auditory sentences. At the same time, the parietal lobe activation associated with spatial processing in the undisturbed driving task decreased by 37% when participants concurrently listened to sentences. The findings show that language comprehension performed concurrently with driving draws mental resources away from the driving and produced deterioration in driving performance, even when it does not require holding or dialing a phone.

Attending to the execution of a complex sensorimotor skill: Expertise differences, choking, and slumps

Rob Gray

Journal of Experimental Psychology: Applied 10:42-54 (2004)

A simulated baseball batting task was used to compare the relative effects of attending to extraneous information (tone frequency) and attending to skill execution (direction of bat movement) on performance and swing kinematics and to evaluate how these effects differ as a function of expertise. The extraneous dual task degraded batting performance in novices but had no significant effect on experts. The skill-focused dual task increased batting error and movement variability for experts but had no significant effect on novice. For expert batters, accuracy in the skill-focused dual task was inversely related to the current level of performance. Expert batters were significant more accurate in the skill-focused dual task when placed under pressure. These findings indicate that the attentional focus varies substantial across and within performers with different levels of expertise.

Reading senseless sentences: Brain potentials reflect semantic incongruity

Marta Kutas and Steven A. Hillyard

Science 207:203-205 (1980)

In a sentence reading task, words that occurred out of context were associated with specific types of event-related potentials. Word that were physically aberrant (larger than normal) elicited a late positive series of potentials, whereas semantically inappropriate words elicits a late negative wave (N400). The N400 wave may be an electrophysiological sign of the “reprocessing” of semantically anomalous information.

Amnesia is a deficit in relational memory

Jennifer D. Ryan, Robert R. Althoff, Stephen Whitlow, and Neal J. Cohen

Psychological Science 11:454-461 (2000)

Eye movements were monitored to assess memory for scenes indirectly (implicitly). Two eye movement-based memory phenomena were observed: (a) the repetition effect, a decrease in sampling of previously viewed scenes compared with new scenes, reflecting memory for those scenes, and (b) the relational manipulation effect, an increase in viewing of the regions where manipulations of relations among scene elements had occurred. In normal control subjects, the relational manipulation effect was expressed only in the absence of explicit awareness of the scene manipulations. Thus, memory representations of scenes contain information about relations among elements of the scenes, at least some of which is not accessible to verbal report. But amnesia patients with severe memory impairment failed to show the relational manipulation effect. Their failure to show any demonstrable memory for relations among the constituent elements of scenes suggests that amnesia involves a fundamental deficit in relational (declarative) memory processing.