The effect of encoding manipulations on neural correlates of episodic retrieval

The present experiments investigated whether the neural correlates of explicit (conscious) retrieval from episodic memory vary qualitatively according to conditions at encoding, as is predicted by current views of the neural basis of memory retrieval. Event-related potential (ERP) correlates of word stem (e.g. MOT_) cued recall were compared for items studied under different encoding conditions. In Experiment 1, encoding was either 'shallow' or 'deep' whereas in Experiment 2 the presentation modality of the study items was either visual or auditory. In both experiments robust ERP memory effects were observed for stems completed with explicitly retrieved items from each encoding condition. The effects varied in their magnitude, such that they were largest when elicited by the more memorable class of item in each experiment. The scalp distributions of the effects did not differ according to encoding condition, a finding which offers no support for the view that retrieval involves the literal reinstatement of neural activity engaged at the time of encoding. The findings instead point to the existence of a set of retrieval operations that are engaged regardless of the conditions under which retrieved information is encoded.

Cholinergic neurotransmission influences covert orientation of visuospatial attention in the rat

RATIONALE

Both monkey and human studies have suggested that attentional orienting may be mediated by the cholinergic neurotransmitter system.

OBJECTIVES

The purpose of the present study was to examine whether the cholinergic agonist (nicotine) and/or antagonist (scopolamine) influence covert orientation in the rat.

METHODS

Rats carried out a visual reaction time task to measure covert orienting of attention following systemic administration of nicotine or scopolamine.

RESULTS

Nicotine reduced reaction times, abolishing the validity effect by differentially speeding the reaction times for invalidly cued targets. Conversely, scopolamine increased the validity effect by disproportionately lengthening reaction times to invalidly cued targets.

CONCLUSIONS

Taken together, these data indicate that cholinergic transmission represents an important neurochemical substrate of visuospatial attention, specifically influencing disengagement or movement of attention.