Event-related brain potentials (ERPs) were recorded from 20 normal participants while they completed a Go/NoGo response inhibition task. Previous ERP studies have implicated the N2 and P3 waveforms as the main indices of processing in this task, and functional brain imaging has shown parietal, prefrontal and anterior cingulate cortices to be involved in response inhibition. 32-channel ERP analysis revealed amplitude differences in the N2/P3 components when stimuli that required a button-press (Go stimuli) were compared with stimuli for which the response had to be withheld (No-Go stimuli), and in N2 and P3 latencies when successful withholds to No-Go stimuli were compared with unsuccessful attempts to inhibit. Further differences in the N2/P3 complex emerged when participants were grouped in terms of a measure of absentmindedness (the Cognitive Failures Questionnaire, CFQ); larger and earlier components were found for high CFQ respondents. We conclude that the latencies of the N2 and P3 may be the critical indicators of active inhibitory processes for this task, suggesting that a pattern of sequential activation rather than altered activity level in key structures may mediate success on the task. In addition, highly absentminded participants exhibited larger components for errors than did less absentminded participants when performing at the same level, which implies that the absentminded may require greater activity in the neural substrates of response inhibition in order to accomplish this task at a comparable level of performance to less absentminded participants.
Damage involving the anterior thalamic and adjacent rostral thalamic nuclei may result in a severe anterograde amnesia, similar to the amnesia resulting from damage to the hippocampal formation. Little is known, however, about the information represented in these nuclei. To redress this deficit, we recorded units in three rostral thalamic nuclei in freely-moving rats [the parataenial nucleus (PT), the anteromedial nucleus (AM) and nucleus reuniens NRe]. We found units in these nuclei possessing previously unsuspected spatial properties. The various cell types show clear similarities to place cells, head direction cells, and perimeter/border cells described in hippocampal and parahippocampal regions. Based on their connectivity, it had been predicted that the anterior thalamic nuclei process information with high spatial and temporal resolution while the midline nuclei have more diffuse roles in attention and arousal. Our current findings strongly support the first prediction but directly challenge or substantially moderate the second prediction. The rostral thalamic spatial cells described here may reflect direct hippocampal/parahippocampal inputs, a striking finding of itself, given the relative lack of place cells in other sites receiving direct hippocampal formation inputs. Alternatively, they may provide elemental thalamic spatial inputs to assist hippocampal spatial computations. Finally, they could represent a parallel spatial system in the brain.
Autonoetic consciousness refers to the ability to mentally transport oneself back in subjective time to relive elements of, or all, of a past event, and is compromised in the early stages of Alzheimer’s disease (AD). Here, we investigate autobiographical memory (ABM) and the recollective experience in amnestic mild cognitive impairment (aMCI). aMCI participants exhibited significant deficits compared with healthy elderly controls for both personal semantic and event detail components of ABM. These decrements were evident across all life epochs for episodic recall. Recall of an event that occurred 1 week previously, was tested in the same spatiotemporal context, and provided the greatest group dissociation, with elderly controls benefitting from a context-dependent memory effect. This reinstantiation of context did not ameliorate the anterograde deficits in the aMCI cohort, nor did it facilitate the mental reliving of these memories for either participant group. Whereas reliving judgments were comparable in both groups, aMCI participants exhibited a compromised capacity to generate vivid, self-referential visual imagery and to re-experience the original emotion of events. These contextual and experiential deficits extended beyond recently encountered events into remote epochs, and suggest a greater level of ABM impairment in aMCI than previously assumed. (JINS, 2010, 16, 546–555.)
Discrete populations of brain cells signal differing types of spatial information. These “spatial cells” are largely confined to a closely-connected network of sites. We describe here, for the first time, cells in the anterior claustrum of the freely-moving rat encoding place, boundary and object information. This novel claustral spatial signal potentially directly modulates a wide variety of anterior cortical regions. We hypothesize that one of the functions of the claustrum is to provide information about body position, boundaries and landmark information, enabling dynamic control of behavior.
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