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Table 3 Theta and gamma abnormalities in people with schizophrenia (PSZ) during working memory processes

From: Disturbed theta and gamma coupling as a potential mechanism for visuospatial working memory dysfunction in people with schizophrenia

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
  1. WM working memory, PSZ people with schizophrenia, MEG magnetoencephalography