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P300 amplitude is insensitive to working memory load in schizophrenia.

Gaspar PA, Ruiz S, Zamorano F, Altayó M, Pérez C, Bosman CA, Aboitiz F - BMC Psychiatry (2011)

Bottom Line: A significant between group difference in P300 amplitude was evidenced only at the low WM load condition (1 -back), being smaller in SZs.SZ subjects display a lower than normal P300 amplitude, which does not vary as a function of memory load.These results are consistent with a general impairment in WM capacity in these patients.

View Article: PubMed Central - HTML - PubMed

Affiliation: Clínica Psiquiátrica Universitaria, Hospital Clínico de la Universidad de Chile, Santiago, Chile. pgaspar@neuro.med.uchile.cl

ABSTRACT

Background: Working memory (WM) tasks usually elicit a P300 ERP component, whose amplitude decreases with increasing WM load. So far, this effect has not been studied in schizophrenics (SZs), a group that is considered to have an aberrant brain connectivity and impairments in WM capacity. The aim of this study was to determine the dependency of the P300 component on WM load in a sample of SZ subjects.

Methods: We recorded 26 subjects (13 SZ patients and their matched controls) with an 80-channel electroencephalogram. Subjects performed an N-back task, a WM paradigm that manipulates the number of items to be stored in memory.

Results: In healthy subjects, P300 amplitude was highest in the low WM load condition, and lowest in both the attentional control condition and the high WM load condition. In contrast, SZs evidenced low P300 amplitude in all conditions. A significant between group difference in P300 amplitude was evidenced only at the low WM load condition (1 -back), being smaller in SZs.

Conclusions: SZ subjects display a lower than normal P300 amplitude, which does not vary as a function of memory load. These results are consistent with a general impairment in WM capacity in these patients.

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N-back task timeline. Trial time sequences for 0-, 1- and 2- back conditions. Black squares represent each stimulus in the task. The symbol * shows the target number during each trial. Inter stimulus interval (ISI): 1.7 sec. Stimulus presentation: 0.2 sec.
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Figure 1: N-back task timeline. Trial time sequences for 0-, 1- and 2- back conditions. Black squares represent each stimulus in the task. The symbol * shows the target number during each trial. Inter stimulus interval (ISI): 1.7 sec. Stimulus presentation: 0.2 sec.

Mentions: WM was assessed using an implicit verbal N-back task [6,14], in which subjects were presented a sequence of digit numbers, and had to determine whether the currently displayed stimulus at any given time had been already displayed in the previous presentation (1-back condition, low WM load); or in the second-to-previous presentation (2-back condition, high WM load) (see figure 1). There was also a control condition (0-back), in which the subject had to recognize a specific digit -zero- when it appeared on the screen. Subjects had to distinguish between targets and non-targets, by pressing two buttons localized in a response palette. Reaction times were recorded after pressing the button. A trial was defined by the presentation of one number followed by the subject's motor response. Trials were presented in 3 blocks; each block representing either the control (0- back) or WM conditions (1- and 2- back). Each block consisted in 180 trials with a 1:1 target/no target relation [6]. Stimuli consisted in a 0.2 sec. presentation of a gray digit (size: 2.6 × 5.2 deg at 65 cm. from the face) located in the center of a black background screen in a 21' CRT monitor. Inter stimulus interval (ISI) were 1.7 sec in all the conditions studied. All the subjects used the dominant hand to respond. Stimulus presentation was implemented using the STIM 1.0 software (Compumedics-Neuroscan®).


P300 amplitude is insensitive to working memory load in schizophrenia.

Gaspar PA, Ruiz S, Zamorano F, Altayó M, Pérez C, Bosman CA, Aboitiz F - BMC Psychiatry (2011)

N-back task timeline. Trial time sequences for 0-, 1- and 2- back conditions. Black squares represent each stimulus in the task. The symbol * shows the target number during each trial. Inter stimulus interval (ISI): 1.7 sec. Stimulus presentation: 0.2 sec.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3049741&req=5

Figure 1: N-back task timeline. Trial time sequences for 0-, 1- and 2- back conditions. Black squares represent each stimulus in the task. The symbol * shows the target number during each trial. Inter stimulus interval (ISI): 1.7 sec. Stimulus presentation: 0.2 sec.
Mentions: WM was assessed using an implicit verbal N-back task [6,14], in which subjects were presented a sequence of digit numbers, and had to determine whether the currently displayed stimulus at any given time had been already displayed in the previous presentation (1-back condition, low WM load); or in the second-to-previous presentation (2-back condition, high WM load) (see figure 1). There was also a control condition (0-back), in which the subject had to recognize a specific digit -zero- when it appeared on the screen. Subjects had to distinguish between targets and non-targets, by pressing two buttons localized in a response palette. Reaction times were recorded after pressing the button. A trial was defined by the presentation of one number followed by the subject's motor response. Trials were presented in 3 blocks; each block representing either the control (0- back) or WM conditions (1- and 2- back). Each block consisted in 180 trials with a 1:1 target/no target relation [6]. Stimuli consisted in a 0.2 sec. presentation of a gray digit (size: 2.6 × 5.2 deg at 65 cm. from the face) located in the center of a black background screen in a 21' CRT monitor. Inter stimulus interval (ISI) were 1.7 sec in all the conditions studied. All the subjects used the dominant hand to respond. Stimulus presentation was implemented using the STIM 1.0 software (Compumedics-Neuroscan®).

Bottom Line: A significant between group difference in P300 amplitude was evidenced only at the low WM load condition (1 -back), being smaller in SZs.SZ subjects display a lower than normal P300 amplitude, which does not vary as a function of memory load.These results are consistent with a general impairment in WM capacity in these patients.

View Article: PubMed Central - HTML - PubMed

Affiliation: Clínica Psiquiátrica Universitaria, Hospital Clínico de la Universidad de Chile, Santiago, Chile. pgaspar@neuro.med.uchile.cl

ABSTRACT

Background: Working memory (WM) tasks usually elicit a P300 ERP component, whose amplitude decreases with increasing WM load. So far, this effect has not been studied in schizophrenics (SZs), a group that is considered to have an aberrant brain connectivity and impairments in WM capacity. The aim of this study was to determine the dependency of the P300 component on WM load in a sample of SZ subjects.

Methods: We recorded 26 subjects (13 SZ patients and their matched controls) with an 80-channel electroencephalogram. Subjects performed an N-back task, a WM paradigm that manipulates the number of items to be stored in memory.

Results: In healthy subjects, P300 amplitude was highest in the low WM load condition, and lowest in both the attentional control condition and the high WM load condition. In contrast, SZs evidenced low P300 amplitude in all conditions. A significant between group difference in P300 amplitude was evidenced only at the low WM load condition (1 -back), being smaller in SZs.

Conclusions: SZ subjects display a lower than normal P300 amplitude, which does not vary as a function of memory load. These results are consistent with a general impairment in WM capacity in these patients.

Show MeSH