Brain state before a memory probe and associative retrieval in older adults

Older individuals' difficulty in remembering events from a particular time and place may be explained by changes in retrieval-related control processes. We investigated how aging affects neural activity leading up to a retrieval probe and how such activity relates to later performance. Electrical brain activity was recorded while healthy younger and older humans memorized visual word pairs consisting of an object word (e.g., doll) preceded by a location word (e.g., garden). Only object words were presented during the memory test, the task being to decide whether an object had been presented earlier and, if so, what location had been paired with it. A warning signal before each test probe alerted to an upcoming object. A sustained negative-going event-related potential deflection preceded objects whose associated location could be remembered, especially in older individuals. The poorer an older individual's associative memory, the bigger was this deflection. Aging thus seems accompanied by changes in anticipatory brain states that relate to recollection. Such states may serve to mobilize control processes that aid the recovery of contextual details

Expected reward modulates encoding-related theta activity before an event

Oscillatory brain activity in the theta frequency range (4–8 Hz) before the onset of an event has been shown to affect the likelihood of successfully encoding the event into memory. Recent work has also indicated that frontal theta activity might be modulated by reward, but it is not clear how reward expectancy, anticipatory theta activity, and memory formation might be related. Here, we used scalp electroencephalography (EEG) to assess the relationship between these factors. EEG was recorded from healthy adults while they memorized a series of words. Each word was preceded by a cue that indicated whether a high or low monetary reward would be earned if the word was successfully remembered in a later recognition test. Frontal theta power between the presentation of the reward cue and the onset of a word was predictive of later memory for the word, but only in the high reward condition. No theta differences were observed before word onset following low reward cues. The magnitude of prestimulus encoding-related theta activity in the high reward condition was correlated with the number of high reward words that were later confidently recognized. These findings provide strong evidence for a link between reward expectancy, theta activity, and memory encoding. Theta activity before event onset seems to be especially important for the encoding of motivationally significant stimuli. One possibility is that dopaminergic activity during reward anticipation mediates frontal theta activity related to memory

The ERP response to the amount of information conveyed by words in sentences

Contains fulltext : 132194.pdf (publisher's version ) (Open Access)Reading times on words in a sentence depend on the amount of information the words convey, which can be estimated by probabilistic language models. We investigate whether event-related potentials (ERPs), too, are predicted by information measures. Three types of language models estimated four different information measures on each word of a sample of English sentences. Six different ERP deflections were extracted from the EEG signal of participants reading the same sentences. A comparison between the information measures and ERPs revealed a reliable correlation between N400 amplitude and word surprisal. Language models that make no use of syntactic structure fitted the data better than did a phrase-structure grammar, which did not account for unique variance in N400 amplitude. These findings suggest that different information measures quantify cognitively different processes and that readers do not make use of a sentence’s hierarchical structure for generating expectations about the upcoming word.11 p

The Relationship between P300 Amplitude and Subsequent Recall for Distinctive Events: Dependence on Type of Distinctiveness Attribute

Distinctive words elicit the P300 component of the event‐related brain potential, and are also likely to be recalled. Previous studies have shown that the larger the P300 elicited by distinctive words, the more likely it is that those words will be recalled. The present study addressed whether this relationship is affected by the manner in which distinctiveness is induced. Distinctiveness was manipulated either by varying the size of the characters in which a word was displayed, or by surrounding the word with a frame at close or far distance. All distinctiveness attributes resulted in improved recall performance. The words whose size was distinctive elicited a large P300, and P300 amplitude was larger for subsequently recalled words. The frame attributes elicited a small P300, and the amplitude of these P300s was not correlated with subsequent recall performance. Instead, a frontal slow wave was correlated with subsequent recall performance in the far frame group. It is concluded that the relationship between P300 amplitude and subsequent recall depends on the type of distinctiveness attribute, and should therefore not be ascribed to a generalized effect of distinctiveness on memory encoding processes

Seeing sounds and hearing colors: An event-related potential study of auditory–visual synesthesia.

Abstract & In auditory-visual synesthesia, sounds automatically elicit conscious and reliable visual experiences. It is presently unknown whether this reflects early or late processes in the brain. It is also unknown whether adult audiovisual synesthesia resembles auditory-induced visual illusions that can sometimes occur in the general population or whether it resembles the electrophysiological deflection over occipital sites that has been noted in infancy and has been likened to synesthesia. Electrical brain activity was recorded from adult synesthetes and control participants who were played brief tones and required to monitor for an infrequent auditory target. The synesthetes were instructed to attend either to the auditory or to the visual (i.e., synesthetic) dimension of the tone, whereas the controls attended to the auditory dimension alone. There were clear differences between synesthetes and controls that emerged early (100 msec after tone onset). These differences tended to lie in deflections of the auditory-evoked potential (e.g., the auditory N1, P2, and N2) rather than the presence of an additional posterior deflection. The differences occurred irrespective of what the synesthetes attended to (although attention had a late effect). The results suggest that differences between synesthetes and others occur early in time, and that synesthesia is qualitatively different from similar effects found in infants and certain auditory-induced visual illusions in adults. In addition, we report two novel cases of synesthesia in which colors elicit sounds, and vice versa. &amp

Context effects on the neural correlates of recognition memory: An electrophysiological study

AbstractEvent-related potentials (ERPs) were recorded during a recognition memory test for previously studied visual objects. Some studied objects were paired with the same context (landscape scenes) as at study, some were superimposed on a different studied context, and some were paired with new contexts. Unstudied objects were paired with either a studied or a new context. Three ERP memory effects were observed: an early effect elicited by all stimuli containing at least one studied component; a second effect elicited only by stimuli in which both object and context had been studied; and a third effect elicited by stimuli containing a studied object. Thus, test stimuli engaged three distinct kinds of memory-related neural activity which differed in their specificity for task-relevant features

Material-specific neural correlates of recollection: objects, words, and faces

It is unclear howneural correlates of episodicmemory retrieval differ depending on the type of material that is retrieved. Here, we used a sourcememory task to compare electrical brain activity for the recollection of three types of stimulus material. At study, healthy adults judged how well visually presented objects, words, and faces fitted with paired auditorily presented names of locations. At test, only visual stimuli were presented. The task was to decide whether an item had been presented earlier and, if so, what location had been paired with the item. Stimulus types were intermixed across trials in Experiment 1 and presented in separate study-test lists in Experiment 2. A graded pattern of memory performance was observed across objects, words, and faces in both experiments. Between 300 and 500 msec, event-related potentials for recollected objects and faces showed a more frontal scalp distribution compared to words in both experiments. Later in the recording epoch, all three stimulus materials elicited recollection effects over left posterior scalp sites. However, these effects extended more anteriorly for objects and faces when stimulus categories were blocked. These findings demonstrate that the neural correlates of recollection are material specific, the crucial difference being between pictorial and verbal material. Faces do not appear to have a special status. The sensitivity of recollection effects to the kind of experimental design suggests that, in addition to type of stimulus material, higher-level control processes affect the cognitive and neural mechanisms underlying episodic retrieval