Human cortical EEG rhythms during long-term episodic memory task. A high-resolution EEG study of the HERA model

Abstract

Many recent neuroimaging studies of episodic memory have indicated an asymmetry in prefrontal involvement, with the left prefrontal cortex more involved than the right in encoding, the right more than the left in retrieval (hemispheric encoding and retrieval asymmetry, or HERA model). In this electroencephalographic (EEG) high-resolution study, we studied brain rhythmicity during a visual episodic memory (recognition) task. The theta (4-6 Hz), alpha (6-12 Hz) and gamma (28-48 Hz) oscillations were investigated during a visuospatial long-term episodic memory task including an encoding (ENC) and retrieval (RET) phases. During the ENC phase, 25 figures representing interiors of buildings ("indoor") were randomly intermingled with 25 figures representing landscapes ("landscapes"). Subject's response was given at left ("indoor") or right ("landscapes") mouse button. During the RET phase (1 h later), 25 figures representing previously presented "indoor" pictures ("tests") were randomly intermingled with 25 figures representing novel "indoor" ("distractors"). Again, a mouse response was required. Theta and alpha EEG results showed no change of frontal rhythmicity. In contrast, the HERA prediction of asymmetry was fitted only by EEG gamma responses, but only in the posterior parietal areas. The ENC phase was associated with gamma EEG oscillations over left parietal cortex. Afterward, the RET phase was associated with gamma EEG oscillations predominantly over right parietal cortex. The predicted HERA asymmetry was thus observed in an unexpected location. This discrepancy may be due to the differential sensitivity of neuroimaging methods to selected components of cognitive processing. The strict relation between gamma response and perception suggests that retrieval processes of long-term memory deeply impinged upon sensory representation of the stored material. © 2004 Elsevier Inc. All rights reserved

Neural Correlates of True and False Memory in Mild Cognitive Impairment

“…For example, the theta range has been defined as 3–5 Hz [58], 3.9–6.8 Hz [21], 4–6 Hz [59], 4–7 Hz [19], 4–7.5 Hz [31], 4–8 Hz [16], and 4.5–7.5 Hz [13]. Similar variation in alpha frequency ranges have also been reported [10], [39], [54].…”

Asymmetric Amplitude Modulations of Brain Oscillations Generate Slow Evoked Responses

“…Posterior alpha activity has been shown to be modulated by cognitive manipulations in a wide variety of tasks. This includes working memory operations (Klimesch et al, 1996;Krause et al, 1996;Jensen et al, 2002;Jokisch and Jensen, 2007;Medendorp et al, 2007), long-term memory retrieval (Klimesch, 1999;Babiloni et al, 2004), directed attention (Worden et al, 2000), and language comprehension (Bastiaansen and Hagoort 2006). In future work, it would be interesting to relate the modulations in alpha activity to the slow components that have been found to be modulated in related tasks (Kutas and Hillyard, 1980;Sanquist et al, 1980;Hagoort and Brown, 2000;Vogel et al, 2005;Takashima et al, 2006;Rugg and Curran, 2007).…”

Effect of Bilateral Eye Movements on Frontal Interhemispheric Gamma EEG Coherence

“…We focused on (a) frontal activity because the frontal lobes have been specifically implicated in episodic memory (e.g., Kavcic et al, 2003) and on (b) gamma-band and theta-band activity because they have been associated with episodic memory processing (e.g., Babiloni et al, 2004;Kaiser and Lutzenberger, 2005;Klimesch et al, 1994). Because alpha has been associated with semantic memory processes (e.g., Klimesch et al, 1994;Mima et al, 2001), we also examined the alpha frequency to rule out a general, nonepisodic memory-related effect of stimuli condition on interhemispheric interaction.…”