Time-dependent memory transformation in hippocampus and neocortex is semantic in nature.

Memories undergo a time-dependent neural reorganization, which is assumed to be accompanied by a transformation from detailed to more gist-like memory. However, the nature of this transformation and its underlying neural mechanisms are largely unknown. Here, we report that the time-dependent transformation of memory is semantic in nature, while we find no credible evidence for a perceptual transformation. Model-based MRI analyses reveal time-dependent increases in semantically transformed representations of events in prefrontal and parietal cortices, while specific pattern representations in the anterior hippocampus decline over time. Posterior hippocampal memory reinstatement, in turn, increases over time and is linked to the semantic gist of the original memory, without a statistically significant link to perceptual details. These findings indicate that qualitative changes in memory over time, associated with distinct representational changes in the neocortex and within the hippocampus, reflect a semantic transformation, which may promote the integration of memories into abstract knowledge structures.

Hemodynamic correlates of emotion regulation in frontal lobe epilepsy patients and healthy participants.

The ability to regulate emotions is indispensable for maintaining psychological health. It heavily relies on frontal lobe functions which are disrupted in frontal lobe epilepsy. Accordingly, emotional dysregulation and use of maladaptive emotion regulation strategies have been reported in frontal lobe epilepsy patients. Therefore, it is of clinical and scientific interest to investigate emotion regulation in frontal lobe epilepsy. We studied neural correlates of upregulating and downregulating emotions toward aversive pictures through reappraisal in 18 frontal lobe epilepsy patients and 17 healthy controls using functional magnetic resonance imaging. Patients tended to report more difficulties with impulse control than controls. On the neural level, patients had diminished activity during upregulation in distributed left-sided regions, including ventrolateral and dorsomedial prefrontal cortex, angular gyrus and anterior temporal gyrus. Patients also showed less activity than controls in the left precuneus for upregulation compared to downregulation. Unlike controls, they displayed no task-related activity changes in the left amygdala, whereas the right amygdala showed task-related modulations in both groups. Upregulation-related activity changes in the left inferior frontal gyrus, insula, orbitofrontal cortex, anterior and posterior cingulate cortex, and precuneus were correlated with questionnaire data on habitual emotion regulation. Our results show that structural or functional impairments in the frontal lobes disrupt neural mechanisms underlying emotion regulation through reappraisal throughout the brain, including posterior regions involved in semantic control. Findings on the amygdala as a major target of emotion regulation are in line with the view that specifically the left amygdala is connected with semantic processing networks.

Noradrenergic arousal after encoding reverses the course of systems consolidation in humans.

It is commonly assumed that episodic memories undergo a time-dependent systems consolidation process, during which hippocampus-dependent memories eventually become reliant on neocortical areas. Here we show that systems consolidation dynamics can be experimentally manipulated and even reversed. We combined a single pharmacological elevation of post-encoding noradrenergic activity through the α2-adrenoceptor antagonist yohimbine with fMRI scanning both during encoding and recognition testing either 1 or 28 days later. We show that yohimbine administration, in contrast to placebo, leads to a time-dependent increase in hippocampal activity and multivariate encoding-retrieval pattern similarity, an indicator of episodic reinstatement, between 1 and 28 days. This is accompanied by a time-dependent decrease in neocortical activity. Behaviorally, these neural changes are linked to a reduced memory decline over time after yohimbine intake. These findings indicate that noradrenergic activity shortly after encoding may alter and even reverse systems consolidation in humans, thus maintaining vividness of memories over time.

How representative are neuroimaging samples? Large-scale evidence for trait anxiety differences between fMRI and behaviour-only research participants.

Over the past three decades, functional magnetic resonance imaging (fMRI) has become crucial to study how cognitive processes are implemented in the human brain. However, the question of whether participants recruited into fMRI studies differ from participants recruited into other study contexts has received little to no attention. This is particularly pertinent when effects fail to generalize across study contexts: for example, a behavioural effect discovered in a non-imaging context not replicating in a neuroimaging environment. Here, we tested the hypothesis, motivated by preliminary findings (N = 272), that fMRI participants differ from behaviour-only participants on one fundamental individual difference variable: trait anxiety. Analysing trait anxiety scores and possible confounding variables from healthy volunteers across multiple institutions (N = 3317), we found robust support for lower trait anxiety in fMRI study participants, consistent with a sampling or self-selection bias. The bias was larger in studies that relied on phone screening (compared with full in-person psychiatric screening), recruited at least partly from convenience samples (compared with community samples), and in pharmacology studies. Our findings highlight the need for surveying trait anxiety at recruitment and for appropriate screening procedures or sampling strategies to mitigate this bias.

Age-dependent semiology of frontal lobe seizures.

INTRODUCTION: Frontal lobe epilepsy is the second most frequent origin of focal epilepsy. Various studies have discussed localizing aspects of ictal signs in frontal lobe epilepsy; the effect of age on semiological manifestations has, however, not been analyzed so far. MATERIAL AND METHODS: We retrospectively analyzed video-documented semiological signs in a cohort of 122 consecutive patients aged 0-70 years (mean age: 24.9 years) with EEG/MR evidence for frontal lobe epilepsy undergoing video-EEG telemetry assessment between 1999 und 2016. RESULTS: In this patient cohort, most common etiologies were focal cortical dysplasia (48%) and tumors (16%). Most frequent ictal manifestations overall were impaired language comprehension (60.3%), unilateral tonic posturing (58.9%), unilateral cloni (46.6%), versive movements (44.5%), vocalization (42.5%) and impaired reactivity to non-verbal stimuli (40.4%). With increasing age, sign of four (p = 0.019), dystonic posturing (p = 0.026), changes in heart rate (p = 0.014) and impaired reactivity to non-verbal stimuli (p = 0.009) occurred significantly more frequently. In contrast, myoclonic components were significantly less frequent observed in the higher age group (p = 0.037). CONCLUSIONS: Frontal lobe seizures can be categorized into different behavioral manifestations related to involved symptomatic brain regions, including clonic, bilateral asymmetric tonic seizures and complex motor phenomena. In this cross-sectional study, we found age-related changes in the frequency of both, motor and non-motor semiological elements. Especially simple lateralized motor signs like dystonic posturing, sign of four and version were more common with increasing age. Age-dependent alterations in phenomenology may reflect maturation in connectivity and seizure propagation within and beyond the frontal lobe, and affect the localizing and lateralizing value of ictal phenomena.