Table 3 Theta and gamma abnormalities in people with schizophrenia (PSZ) during working memory processes
Authors & Year of Publication | Subjects | Measure | Region of Brain/Scalp Examined | Task Performed/Behavior during Measurement | WM Subprocess(es) Analyzed | Relevant Findings | Conclusions |
|---|---|---|---|---|---|---|---|
Theta abnormalities | |||||||
i. Schmiedt, Brand, Hildebrandt, & Başar-Eroğlu (2005) [113] | - 10 inpatient PSZ (aged 34 ± 6 years) - 10 healthy controls (aged 24 ± 4 years) | Scalp EEG | Fz, Cz, Pz, Oz, F3, F4, T5, T6 | Visual variable N-back with action monitoring/rule-switching | Maintenance, encoding | - Widespread reduced theta-amplitude in PSZ during maintenance compared to controls - Enhanced amplitude in PSZ at left temporal locations in first 250 ms post-stimulus - PSZ failed to modulate frontal theta amplitude with task changes, whereas controls’ amplitudes increased with task difficulty | - Increased temporal theta indicates pathological processes in frontal and temporal regions in PSZ - Failure to modulate theta suggests deficits in executive processes related to WM |
ii. Haenschel et al. (2009) [29] | - 14 patients with early onset schizophrenia (onset prior to age 18; 5 females, aged 17.76 ± 1.44 years) - 14 controls (aged 17.37 ± 1.41 years) | Scalp EEG | Scalp-wide | Delayed visual discrimination task | Encoding, maintenance and retrieval | - PSZ showed reduced theta-amplitudes during encoding and retrieval as compared to controls - Evoked posterior theta decreased with increasing WM load during encoding in controls but not PSZ - Evoked anterior theta during encoding predictive of performance in controls but not PSZ | - Reduced evoked theta during encoding may reflect impaired phase resetting to stimuli; reductions during retrieval may reflect a failure in PSZ to recognize previously encountered stimuli - Lack of decrease in theta amplitude in PSZ may reflect deficient responses to initial stimuli as well as habituation processes |
iii. Missonnier et al. (2012) [114] | - 15 patients with first-episode psychosis (3 females, aged 21.9 ± 2.6 years, 6 diagnosed schizophreniform, 9 schizophrenia) - 18 controls (9 females, aged 24.4 ± 1.5 years) | Scalp EEG | Scalp-wide | - Visual oddball task - Visual N-back task - Simple detection task | Maintenance, encoding | - PSZ showed increased sustained theta amplitudes in frontal areas for the retention period of detection and 1-back tasks, as well as delayed maximums of phasic event-related theta synchronization, compared to controls | PSZ fail to appropriately modulate brain activation to address increasing demands on WM |
iv. Griesmayr et al. (2014) [115] | - 21 PSZ (5 females, aged 22 to 46.02 years, mean age = 31.96 years) - 21 healthy controls (5 females, aged 20.05 to 47.02 years, mean age = 31.55) | Scalp EEG | Scalp-wide | Visuospatial delayed match-to-sample task with manipulation | Maintenance/manipulation | - Reduced phase-synchrony in PSZ: primarily reductions between frontal and posterior regions, but reductions within posterior areas also observed during high WM-load - PSZ showed increased theta amplitude for manipulation versus maintenance processes; controls showed no such difference - Controls demonstrated increase in posterior theta amplitude with increasing load; PSZ did not | - Deficits in theta phase-synchrony represent binding difficulties in PSZ - Modulation of theta amplitude in PSZ may suggest inefficient allocation of cognitive resources rather than pure WM processes |
Gamma abnormalities | |||||||
v. Kissler, Müller, Fehr, Rockstroh, & Elbert (2000) [116] | - 15 PSZ (4 females, aged 30.2 ± 6.5 years) - 15 healthy controls (4 females, aged 35.8 ± 9.4 years) | MEG | Whole-head | Mental arithmetic task | Manipulation | Controls showed increases in frontotemporal gamma activity during arithmetic; PSZ did not, but instead showed reduced gamma-amplitudes at temporal and occipital areas | - Gamma-activity can be generated without external stimuli - Schizophrenia may be associated with abnormalities in thalamocortical loop |
vi. Başar-Eroğlu et al. (2007) [117] | - 10 PSZ (aged 34 ± 6 years) - 10 healthy controls (aged 24 ± 4 years) | Scalp EEG | Fz, Cz, Pz, Oz, F3, F4, T5, T6 | Visual variable N-back with action monitoring/rule-switching | Maintenance, encoding/retrieval | - Trend towards increased gamma-power across scalp in PSZ relative to controls - Controls showed gradual increase in gamma during maintenance, while PSZ showed increased gamma amplitudes pre- and post-stimuli - Controls’ gamma responses increased with WM load, while PSZs’ did not | PSZ may need to inefficiently initiate cognitive control on simple tasks that controls may complete via automated processes |
vii. Haenschel et al. (2009) [29] | - 14 patients with early onset schizophrenia (onset prior to age 18; 5 females, aged 17.76 ± 1.44 years) - 14 controls (aged 17.37 ± 1.41 years) | Scalp EEG | Scalp-wide | Delayed visual discrimination task | Encoding, maintenance and retrieval | - PSZ showed reductions in induced gamma-power during retrieval over both anterior and posterior sites as compared to controls - Controls showed an increase in induced gamma amplitudes during late maintenance from load 1 to 2 and a subsequent decrease from 2 to 3; PSZ showed the opposite pattern | - PSZ may have difficulties effectively retrieving stimulus representations - Differing patterns of gamma modulation during maintenance may reflect a lower storage capacity limit in PSZ as compared to controls |
viii. Barr et al. (2010) [118] | - 24 participants with schizophrenia (n = 19) or schizoaffective disorder (n = 5); 10 females, aged 37.09 ± 11.04 years) - 24 healthy controls (11 females, aged 37.71 ± 10.12 years) | Scalp EEG | Scalp-wide; only frontal electrodes used for evoked gamma analyses | Visual N-back task | Maintenance | Increased evoked gamma-power over frontal sites as well as failure to modulate gamma-power with increasing WM load in PSZ as compared to healthy controls | PSZ may allocate attentional resources inefficiently |
ix. Chen et al. (2014) [119] | - 12 PSZ (3 females, aged 31 ± 10.79 years) - 12 controls (6 females, aged 33.08 ± 8.23 years) | Scalp EEG | Scalp-wide; only frontal electrodes used for gamma-analyses | Modified Sternberg paradigm | Encoding, maintenance, retrieval | - PSZ showed reduced frontal (F3) gamma amplitudes during all three WM stages as compared to controls - Gamma amplitudes correlated with duration of illness in PSZ - PSZ failed to modulate gamma amplitudes across all WM stages as compared to controls (Supplementary materials) | - PSZ demonstrate impaired inter-regional connections involving \the frontal lobe - PSZ both lack and misallocate cognitive resources as compared to controls |