The application of TMS in Memory Studies
TMS can be used as a research tool to investigate memory formation and retention. In the case of long-term memory TMS allows one to disentangle the effects of encoding and retrieval more easily than in the case of lesion studies.
Ongoing research
Investigations of verbal, visual and spatial working memory as well as episodic memory are carried out using TMS. Working memory is the ability to retain and manipulate information over a short time period (Baddeley 1992) and while extensive experimental literature indicates that the PFC plays a crucial role in working memory function, there is an ongoing debate about the organization of WM processes within this region (Petrides 2005).
The first study in this field dealt with nondeclarative motor-memory and showed an increased error rate in a delayed-response motor task after rTMS to the right and left dorsolateral PFC, but not after stimulation of the motor cortex or in absence of stimulation (Pascual-Leone and Hallet 1994).
Episodic memory allows the encoding, long-term storage and intentional recollection of unique events (Baddeley et al. 2001). Some neuroimaging studies suggest that lateralization of prefrontal cortex activation associated with episodic memory declines with aging; The effects of rTMS applied to the left or right DLPFC on a visuospatial recognition memory task were compared in a population of healthy subjects divided into two classes of age (<45 and >50 years). In younger subjects, rTMS of the right DLPFC interfered with retrieval more than left DLPFC stimulation. The asymmetry of this effect was reduced with aging and bilateral interference effects were found on memory performance. These data suggest that the bilateral engagement of the DLPFC may have a compensatory role on episodic memory across the life span (Rossi et al., 2004).
Regarding motor memory, studies implemented so far have mostly focused on the ability of TMS and tDCS to elicit relatively short lasting motor improvements and the mechanisms underlying these changes have been only partially investigated. TMS could be used to modulate motor learning and memory formation in healthy humans and potentially in patients with neurological and psychiatric disorders (Reis et al. 2008). Positive effects of rTMS on naming abilities have been reported in patients with chronic aphasia (Naeser et al. 2005).
References
- Reis et al. Brain Stimul. 2008
- Naeser et al. 2005
- Rossi et al., 2004
- Baddeley et al. 2001
- Baddeley 1992
- Pascual-Leone and Hallet 1994
- Petrides 2005
