Hippocampal subfield associations with memory depend on stimulus modality and retrieval mode

Hippocampal atrophy is a well-known feature of age-related memory decline, and hippocampal subfields may contribute differently to this decline. In this cross-sectional study, we investigated the associations between hippocampal subfield volumes and performance in free recall and recognition memory tasks in both verbal and visual modalities in older adults without dementia. We collected MRIs from 97 (41 males) right-handed participants aged over 60. We segmented the right and left hippocampi into (i) dentate gyrus and cornu ammonis 4 (DG/CA4); (ii) CA2 and CA3 (CA2/CA3); (iii) CA1; (iv) strata radiatum, lacunosum and moleculare; and (v) subiculum. Memory was assessed with verbal free recall and recognition tasks, as well as visual free recall and recognition tasks. Amyloid-β and hippocampal tau positivity were assessed using [18F]AZD4694 and [18F]MK6240 PET tracers, respectively. The verbal free recall and verbal recognition performances were positively associated with CA1 and strata radiatum, lacunosum and moleculare volumes. The verbal free recall and visual free recall were positively correlated with the right DG/CA4. The visual free recall, but not verbal free recall, was also associated with the right CA2/CA3. The visual recognition was not significantly associated with any subfield volume. Hippocampal tau positivity, but not amyloid-β positivity, was associated with reduced DG/CA4, CA2/CA3 and strata radiatum, lacunosum and moleculare volumes. Our results suggest that memory performances are linked to specific subfields. CA1 appears to contribute to the verbal modality, irrespective of the free recall or recognition mode of retrieval. In contrast, DG/CA4 seems to be involved in the free recall mode, irrespective of verbal or visual modalities. These results are concordant with the view that DG/CA4 plays a primary role in encoding a stimulus' distinctive attributes, and that CA2/CA3 could be instrumental in recollecting a visual memory from one of its fragments. Overall, we show that hippocampal subfield segmentation can be useful for detecting early volume changes and improve our understanding of the hippocampal subfields' roles in memory.

Mapping neurotransmitter systems to the structural and functional organization of the human neocortex

Neurotransmitter receptors support the propagation of signals in the human brain. How receptor systems are situated within macro-scale neuroanatomy and how they shape emergent function remain poorly understood, and there exists no comprehensive atlas of receptors. Here we collate positron emission tomography data from more than 1,200 healthy individuals to construct a whole-brain three-dimensional normative atlas of 19 receptors and transporters across nine different neurotransmitter systems. We found that receptor profiles align with structural connectivity and mediate function, including neurophysiological oscillatory dynamics and resting-state hemodynamic functional connectivity. Using the Neurosynth cognitive atlas, we uncovered a topographic gradient of overlapping receptor distributions that separates extrinsic and intrinsic psychological processes. Finally, we found both expected and novel associations between receptor distributions and cortical abnormality patterns across 13 disorders. We replicated all findings in an independently collected autoradiography dataset. This work demonstrates how chemoarchitecture shapes brain structure and function, providing a new direction for studying multi-scale brain organization.

Cholinergic system changes in Parkinson's disease: emerging therapeutic approaches

In patients with Parkinson's disease, heterogeneous cholinergic system changes can occur in different brain regions. These changes correlate with a range of clinical features, both motor and non-motor, that are refractory to dopaminergic therapy, and can be conceptualised within a systems-level framework in which nodal deficits can produce circuit dysfunctions. The topographies of cholinergic changes overlap with neural circuitries involved in sleep and cognitive, motor, visuo-auditory perceptual, and autonomic functions. Cholinergic deficits within cognition network hubs predict cognitive deficits better than do total brain cholinergic changes. Postural instability and gait difficulties are associated with cholinergic system changes in thalamic, caudate, limbic, neocortical, and cerebellar nodes. Cholinergic system deficits can involve also peripheral organs. Hypercholinergic activity of mesopontine cholinergic neurons in people with isolated rapid eye movement (REM) sleep behaviour disorder, as well as in the hippocampi of cognitively normal patients with Parkinson's disease, suggests early compensation during the prodromal and early stages of Parkinson's disease. Novel pharmacological and neurostimulation approaches could target the cholinergic system to treat motor and non-motor features of Parkinson's disease.

FEOBV-PET to quantify cortical cholinergic denervation in AD: Relationship to basal forebrain volumetry

BACKGROUND AND PURPOSE

Fluorine-18-fluoroethoxybenzovesamicol([¹⁸ F]-FEOBV) is a PET radiotracer previously used in neurodegenerative diseases to quantify brain cholinergic denervation. The current exploratory study aimed at verifying the reliability of such an approach in Alzheimer's disease (AD) by demonstrating its concordance with MRI volumetry of the cholinergic basal forebrain (ChBF).

METHODS

The sample included 12 participants evenly divided between healthy volunteers and patients with AD. All participants underwent MRI ChBF volumetry and PET imaging with [¹⁸ F]-FEOBV. Comparisons were made between the two groups, and partial correlations were performed in the AD patients between [¹⁸ F]-FEOBV uptake in specific cortical regions of interest (ROIs) and volumetry of the corresponding ChBF subareas, which include the nucleus basalis of Meynert (Ch4), and the medial septum/vertical limb of the diagonal band of Broca (Ch1/2).

RESULTS

Patients with AD showed both lower ChBF-Ch4 volumetric values and lower [¹⁸ F]-FEOBV cortical uptake than healthy volunteers. Volumes of the Ch4 subdivision were significantly correlated with the [¹⁸ F]-FEOBV uptake values observed in the relevant ROIs. Volumes of the Ch1/2, which remains relatively unaffected in AD, did not correlate with [¹⁸ F]-FEOBV uptake in the hippocampus, nor in any cortical area.

CONCLUSION

These results suggest that cortical cholinergic denervation as measured with [¹⁸ F]-FEOBV PET is proportional to ChBF atrophy measured by MRI-based volumetry, further supporting the reliability and validity of [¹⁸ F]-FEOBV PET to quantify cholinergic degeneration in AD.

Over facilitation of unadapted cognitive processes in obsessive compulsive disorder as assessed with the computerized mirror pointing task

Response inhibition has been suggested to be dysfunctional in obsessive-compulsive disorder (OCD). However, this process involves intentional cognitive control, which does not correspond to the automatic emergence of stereotyped thoughts and behaviours usually reported by patients with OCD. In the present study, the excessive facilitation of unintentional processes was assessed in OCD by using the Computerized Mirror Pointing Task (CMPT). Seventy-six volunteers participated in this study, including 39 patients with OCD and 37 healthy controls. The CMPT was administered to all participants, and a score of appropriateness of the sensorimotor adaptation to the mirror inversion was computed from the initial deviation angle (IDA), that precedes the intentional readjustment of movement. Results showed that throughout the 40 trials of the CMPT, the IDA score remained significantly abnormal in patients with OCD in comparison with control participants. Further analyses of IDA scores in OCD revealed a clear tendency to keep a natural visuomotor processing that is rigid and unadapted to the mirror condition. Irrespective of the physical requirements of the environment, patients with OCD showed a strong tendency to initiate movements as per a previously consolidated - although unadapted - sensorimotor mapping. This suggests a tendency for an excessive facilitation of unintentional stereotyped processes. Further studies should be conducted on this question by using tasks sensitive to cognitive processes other than visuo-spatial abilities.

Sensorimotor adaptation in Parkinson's disease: evidence for a dopamine dependent remapping disturbance

Sensorimotor adaptation is thought to involve a remapping of the kinematic and kinetic parameters associated with movements performed within a changing environment. Patients with Parkinson's disease (PD) are known to be affected on this type of learning process, although the specific role of dopamine depletion in these deficits has not yet been elucidated. The present study was an attempt to clarify whether dopamine depletion in PD may directly affect the capacity to internally reorganize the visuomotor remapping of a distorted environment. Fourteen PD patients were tested twice, while they were treated and while they were withdrawn from their regular levodopa treatment. Fourteen control subjects were also enrolled and tested twice. Two parallel forms of the Computed Mirror Pointing Task (CMPT), requiring making a reaching movement in a visually transformed environment (mirror inversion), were administered to each participant. Each of them had to perform 40 trials at each of the 2 testing sessions. At each trial, sensorimotor adaptation was evaluated by the initial direction angle (IDA), which reflects the direction of movement before any visually guided readjustment. Results revealed no IDA difference at baseline, between control subject and PD patients, whether they were treated or not. In all group, IDA values at that time were large, reflecting a tendency to make movements according to the real life visuomotor mapping (based on the natural direct vision). However, striking differences appeared during sensorimotor learning, in that IDA reduction along trials was poorer in patient not treated with levodopa than both control subjects and the same PD patient treated with levodopa. No difference was observed between the treated PD patients and control subjects. Given that IDA is thought to reflect the internal representation of the visuomotor mapping, it is concluded that dopamine depletion in PD would affects sensorimotor adaptation, in that it facilitates old and poorly adapted movements (real life mapping), instead of new and more adapted ones (mirror transformed mapping).

Raclopride-induced motor consolidation impairment in primates: role of the dopamine type-2 receptor in movement chunking into integrated sequences

Results obtained in patients with schizophrenia have shown that antipsychotic drugs may induce motor learning deficits correlated with the striatal type-2 dopamine receptors (D(2)R) occupancy. Other findings suggest that the role of the striatum in motor learning could be related to a process of "chunking" discrete movements into motor sequences. We therefore hypothesized that a D(2)R blocking substance, such as raclopride, would affect motor learning by specifically disrupting the grouping of movements into sequences. Two monkeys were first trained to perform a baseline-overlearned sequence (Seq. A) drug free. Then, a new sequence was learned (Seq. B) and the overlearned sequence was recalled OFF-drug (Seq. A recall OFF-drug). The effect of raclopride was then assessed on the learning of a third sequence (Seq. C), and on the recall of the overlearned sequence (Seq. A recall ON-drug). Results showed that performance related to the overlearned sequence remained the same in the three experimental conditions (Seq. A, Seq. A recall OFF-drug, Seq. A recall ON-drug), whether the primates received raclopride or not. On the other hand, new sequence learning was significantly affected during raclopride treatment (Seq. C), when compared with new sequence learning without the effect of any drug (Seq. B). Raclopride-induced disturbances consisted in performance fluctuations, which persisted even after many days of trials, and prevented the monkeys from reaching a stable level of performance. Further analyses also showed that these fluctuations appeared to be related to monkeys' inability to group movements into single flowing motor sequences. The results of our study suggest that dopamine is involved in the stabilization or consolidation of motor performances, and that this function would involve a chunking of movements into well-integrated sequences.

Procedural learning in schizophrenia can reflect the pharmacologic properties of the antipsychotic treatments

BACKGROUND

Conventional and atypical antipsychotics have different affinities for D2 receptors, and these receptors are principally located in the striatum. Given that this cerebral structure was previously found to play a major role in procedural learning, the antipsychotic treatment in schizophrenia may be determinant for the procedural learning profile of these patients.

OBJECTIVE

The current study was aimed at verifying whether procedural learning differs in patients with schizophrenia treated with conventional antipsychotics and patients treated with atypical antipsychotics.

METHOD

Forty-five patients with schizophrenia were divided into 3 different groups according to their pharmacologic treatment: (1) haloperidol, a classical neuroleptic with high D2 receptor affinity; (2) clozapine, an atypical neuroleptic with practically no D2 receptor affinity; and (3) risperidone, an atypical neuroleptic that nevertheless shows high D2 receptor affinity. Patients were compared to 35 control subjects on a visuomotor procedural learning task (mirror drawing).

RESULTS

All patients were able to learn the task. However, those treated with haloperidol showed some degree of learning impairment, while those treated with clozapine or risperidone did not show this impairment. In addition, performance per se, regardless of the learning, was found to be affected in the haloperidol and risperidone, but not in the clozapine groups.

CONCLUSION

Procedural learning in schizophrenia may be differentially affected, depending on the pharmacologic profiles of the antipsychotics used for the treatment of this illness.

The effect of gamma-hydroxybutyrate on nocturnal and diurnal sleep of normal subjects: further considerations on REM sleep-triggering mechanisms

Gamma-hydroxybutyrate (GHB) is a drug currently used to treat narcolepsy. The present study documents its effect on sleep organization in healthy subjects. GHB and a placebo were given at bedtime and before a morning nap in a double-blind fashion. GHB administered before nocturnal or diurnal sleep increases stages 3 and 4 and decreases stage 1 non-rapid eye movement (NREM) sleep. In addition, GHB improves REM efficiency at night and reduces wake time after sleep onset when administered before a morning nap recording. GHB also slightly decreases REM latency when administered in the morning, and this effect is correlated with age. Hypotheses regarding mechanisms of action GHB and the involvement of hypothalamic structures in the regulation of REM sleep are discussed.