Disturbed temporal dynamics of episodic retrieval activity with preserved spatial activity pattern in amnestic mild cognitive impairment: A simultaneous EEG-fMRI study

Background Episodic memory (EM) deficit is the core cognitive dysfunction of amnestic mild cognitive impairment (aMCI). However, the episodic retrieval circuit detected by functional MRI (fMRI) appears preserved in aMCI subjects. To address this discrepancy, this study employed simultaneous electroencephalography (EEG)-fMRI recording to determine whether temporal dynamics of brain episodic retrieval activity were disturbed in patients with aMCI. Methods Twenty-six aMCI and 29 healthy control (HC) subjects completed a word-list memory retrieval task during simultaneous EEG-fMRI. The retrieval success activation pattern was detected with fMRI analysis, and the familiarity- and recollection-related components of episodic retrieval activity were identified using event-related potential (ERP) analysis. The fMRI-constrained ERP analysis explored the temporal dynamics of brain activity in the retrieval success pattern, and the ERP-informed fMRI analysis detected fMRI correlates of the ERP components related to familiarity and recollection processes. Results The two groups exhibited similar retrieval success patterns in the bilateral posteromedial parietal cortex, the left inferior parietal lobule (IPL), and the left lateral prefrontal cortex (LPFC). The fMRI-constrained ERP analysis showed that the aMCI group did not exhibit old/new effects in the IPL and LPFC that were observed in the HC group. In addition, the aMCI group showed decreased fMRI activity in the precuneus and left hippocampus related to ERP familiarity and recollection components, respectively. Conclusions This study identified disturbed temporal dynamics in episodic retrieval activity with a preserved spatial activity pattern in aMCI. Taken together, the simultaneous EEG-fMRI technique demonstrated the potential to identify individuals with a high risk of cognitive deterioration.

Orthonasal Smell

The brain creates the aroma perception through a series of steps, through the olfactory bulb to the olfactory cortex and to the highest levels in our frontal lobes. It first represents the aroma molecules as a spatial activity pattern in the olfactory bulb, virtually an “aroma image” analogous to a visual image in the brain. The smell image is enhanced by lateral inhibition, similar to contrast enhancement as we described in vision. In smell, the image can be modified depending on whether we are hungry or full. It cautions the wine taster to avoid these extremes and be in a good behavioral state.

Temporal and spatial activity of the key-hole limpet Fissurella crassa (Mollusca: Gastropoda) in the eastern Pacific

An automated photographic technique was used to collect quantitative information on the activity patterns of Fissurella crassa under heavy-exposed sea conditions.The activity of this key-hole limpet was confined to nocturnal low tides. Total length of excursions was significantly greater during spring tides than neap tides, as was the maximum distance reached from the refuge. Total duration of excursions and their average speed did not vary significantly according to the spring/neap cycle. While the direction angle of excursions relative to the refuge was not influenced significantly by the spring/neap cycle, the lowest zone within the intertidal was reached by F. crassa during spring low tides only.Fissurella crassa showed a spatial activity pattern fluctuating intra/inter-individually between a central place foraging and a ranging strategy, with a marked propensity for the former. Looped excursions were characterized by higher speed for the movements away and toward the limpet's refuge, than the movements at maximum distance from the refuge. As the outward and inward branches of looped excursions often overlapped extensively, trail-following is suggested as the main mechanism of orientation used by F. crassa to relocate the refuge.