Correlates of Theta and Gamma Activity during Visuospatial Incidental/Intentional Encoding and Retrieval Indicate Differences in Processing in Young and Elderly Healthy Participants.

Incidental visuospatial learning acquired under incidental conditions is more vulnerable to aging than in the intentional case. The theta and gamma correlates of the coding and retrieval of episodic memory change during aging. Based on the vulnerability of incidental coding to aging, different theta and gamma correlates could occur under the incidental versus intentional coding and retrieval of visuospatial information. Theta and gamma EEG was recorded from the frontotemporal regions, and incidental/intentional visuospatial learning was evaluated in young (25-60 years old) and elderly (60-85 years old) participants. The EEG recorded during encoding and retrieval was compared between incidental low-demand, incidental high-demand, and intentional conditions through an ANCOVA considering the patient's gender, IQ, and years of schooling as covariates. Older adults exhibited worse performances, especially in place-object associations. After the intentional study, older participants showed a further increase in false-positive errors. Higher power at the theta and gamma bands was observed for frontotemporal derivations in older participants for both encoding and retrieval. Under retrieval, only young participants had lower power in terms of errors compared with correct responses. In conclusion, the different patterns of power and coherence support incidental and intentional visuospatial encoding and retrieval in young and elderly individuals. The correlates of power with behavior are sensitive to age and performance.

EEG alpha and theta time-frequency structure during a written mathematical task.

Since the first electroencephalogram (EEG) was obtained, there have been many possibilities to use it as a tool to access brain cognitive dynamics. Mathematical (Math) problem solving is one of the most important cortical processes, but it is still far from being well understood. EEG is an inexpensive and simple indirect measure of brain operation, but only recently has low-cost equipment (mobile EEG) allowed sophisticated analyses in non-clinical settings. The main purpose of this work is to study EEG activation during a Math task in a realistic environment, using mobile EEG. A matching pursuit (MP)-based signal analysis technique was employed, since MP properties render it a priori suitable to study induced EEG activity over long time sequences, when it is not tightly locked to a given stimulus. The study sample comprised sixty healthy volunteers. Unlike the majority of previous studies, subjects were studied in a sitting position with their eyes open. They completed a written Math task outside the EEG lab, wearing a mobile EEG device (EPOC+). Theta [4 Hz-7.5 Hz], alpha (7.5 Hz-13 Hz] and 0.5 Hz micro-bands in the [0.5 Hz-20 Hz] range were studied with a low-density stochastic MP dictionary. Over 1-min windows, ongoing EEG alpha and theta activity was decomposed into numerous MP atoms with median duration around 3 s, similar to the duration of induced, time-locked activity obtained with event-related (des)synchronization (ERS/ERD) studies. Relative to Rest, there was lower right-side and posterior MP alpha atom/min during Math, whereas MP theta atom/min was significantly higher on anteriorly located electrodes, especially on the left side. MP alpha findings were particularly significant on a narrow range around 10 Hz-10.5 Hz, consistent with FFT alpha peak findings from ERS/ERD studies. With a streamlined protocol, these results replicate previous findings of EEG alpha and theta activation obtained during Math tasks with different signal analysis techniques and in different time frames. The efficient application to real-world, noisy EEG data with a low-resolution stochastic MP dictionary shows that this technique is very encouraging. These results provide support for studies of mathematical cognition with mobile EEG and matching pursuit.

Afferent and efferent connections of the interpeduncular nucleus with special reference to circuits involving the habenula and raphe nuclei.

The habenula is an epithalamic structure differentiated into two nuclear complexes, medial (MHb) and lateral habenula (LHb). Recently, MHb together with its primary target, the interpeduncular nucleus (IP), have been identified as major players in mediating the aversive effects of nicotine. However, structures downstream of the MHb-IP axis, including the median (MnR) and caudal dorsal raphe nucleus (DRC), may contribute to the behavioral effects of nicotine. The afferent and efferent connections of the IP have hitherto not been systematically investigated with sensitive tracers. Thus, we placed injections of retrograde or anterograde tracers into different IP subdivisions or the MnR and additionally examined the transmitter phenotype of major IP and MnR afferents by combining retrograde tract tracing with immunofluorescence and in situ hybridization techniques. Besides receiving inputs from MHb and also LHb, we found that IP is reciprocally interconnected mainly with midline structures, including the MnR/DRC, nucleus incertus, supramammillary nucleus, septum, and laterodorsal tegmental nucleus. The bidirectional connections between IP and MnR proved to be primarily GABAergic. Regarding a possible topography of IP outputs, all IP subnuclei gave rise to descending projections, whereas major ascending projections, including focal projections to ventral hippocampus, ventrolateral septum, and LHb originated from the dorsocaudal IP. Our findings indicate that IP is closely associated to a distributed network of midline structures that modulate hippocampal theta activity and forms a node linking MHb and LHb with this network, and the hippocampus. Moreover, they support a cardinal role of GABAergic IP/MnR interconnections in the behavioral response to nicotine.

Two Different Populations within the Healthy Elderly: Lack of Conflict Detection in Those at Risk of Cognitive Decline.

During healthy aging, inhibitory processing is affected at the sensorial, perceptual, and cognitive levels. The assessment of event-related potentials (ERPs) during the Stroop task has been used to study age-related decline in the efficiency of inhibitory processes. Studies using ERPs have found that the P300 amplitude increases and the N500 amplitude is attenuated in healthy elderly adults compared to those in young adults. On the other hand, it has been reported that theta excess in resting EEG with eyes closed is a good predictor of cognitive decline during aging 7 years later, while a normal EEG increases the probability of not developing cognitive decline. The behavioral and ERP responses during a Counting-Stroop task were compared between 22 healthy elderly subjects with normal EEG (Normal-EEG group) and 22 healthy elderly subjects with an excess of EEG theta activity (Theta-EEG group). Behaviorally, the Normal-EEG group showed a higher behavioral interference effect than the Theta-EEG group. ERP patterns were different between the groups, and two facts are highlighted: (a) the P300 amplitude was higher in the Theta-EEG group, with both groups showing a P300 effect in almost all electrodes, and (b) the Theta-EEG group did not show an N500 effect. These results suggest that the diminishment in inhibitory control observed in the Theta-EEG group may be compensated by different processes in earlier stages, which would allow them to perform the task with similar efficiency to that of participants with a normal EEG. This study is the first to show that healthy elderly subjects with an excess of theta EEG activity not only are at risk of developing cognitive decline but already have a cognitive impairment.

Septal serotonin depletion in rats facilitates working memory in the radial arm maze and increases hippocampal high-frequency theta activity.

Hippocampal theta activity, which is strongly modulated by the septal medial/Broca׳s diagonal band neurons, has been linked to information processing of the hippocampus. Serotonin from the medial raphe nuclei desynchronises hippocampal theta activity, whereas inactivation or a lesion of this nucleus induces continuous and persistent theta activity in the hippocampus. Hippocampal serotonin depletion produces an increased expression of high-frequency theta activity concurrent with the facilitation of place learning in the Morris maze. The medial septum-diagonal band of Broca complex (MS/DBB) has been proposed as a key structure in the serotonin modulation of theta activity. We addressed whether serotonin depletion of the MS/DBB induces changes in the characteristics of hippocampal theta activity and whether the depletion is associated with learning in a working memory spatial task in the radial arm maze. Sprague Dawley rats were depleted of 5HT with the infusion of 5,7-dihydroxytriptamine (5,7-DHT) in MS/DBB and were subsequently trained in the standard test (win-shift) in the radial arm, while the CA1 EEG activity was simultaneously recorded through telemetry. The MS/DBB serotonin depletion induced a low level of expression of low-frequency (4.5-6.5Hz) and a higher expression of high-frequency (6.5-9.5Hz) theta activity concomitant to a minor number of errors committed by rats on the working memory test. Thus, the depletion of serotonin in the MS/DBB caused a facilitator effect on working memory and a predominance of high-frequency theta activity.