Dissociating neuromodulatory effects of diazepam on episodic memory encoding and executive function

Area of Science:

• Neuroscience
• Cognitive Psychology
• Pharmacology

Background:

• Benzodiazepines, including diazepam, are known to impair episodic memory encoding.
• Executive function deficits are also reported with benzodiazepine use.
• This study investigates whether executive function impairments are secondary to memory deficits or distinct drug effects.

Purpose of the Study:

• To examine the neuroanatomical correlates of diazepam's effects on executive function and episodic memory tasks.
• To determine if similarities in brain activity reflect common drug effects or if task-specific changes indicate distinct functional impacts.
• To differentiate the effects of diazepam on memory encoding versus executive ordering tasks.

Main Methods:

• Positron emission tomography (PET) was used in 12 healthy volunteers.
• A between-subjects design administered placebo or 10 mg diazepam.
• A 2x2 factorial design assessed memory encoding and executive function (stimulus ordering) during scanning.

Main Results:

• Diazepam decreased bilateral prefrontal and temporal cortex activity compared to placebo.
• Left dorsal prefrontal cortex activity was attenuated during memory encoding.
• Left frontal opercular activity was attenuated during the ordering task.

Conclusions:

• A neuroanatomical dissociation indicates distinct functional effects of diazepam on encoding and ordering tasks.
• The observed effects on ordering tasks are not secondary to diazepam's impact on episodic memory.
• Diazepam exerts real and distinct effects on executive function separate from its mnemonic impairments.