Decreased processing speed might account for working memory span deficit in schizophrenia, and might mediate the associations between working memory span and clinical symptoms.
OBJECTIVE
Verbal working memory span is decreased in patients with schizophrenia, and this might contribute to impairment in higher cognitive functions as well as to the formation of certain clinical symptoms. Processing speed has been identified as a crucial factor in cognitive efficiency in this population. We tested the hypothesis that decreased processing speed underlies the verbal working memory deficit in patients and mediates the associations between working memory span and clinical symptoms.


METHODS
Forty-nine schizophrenia inpatients recruited from units for chronic and acute patients, and forty-five healthy participants, were involved in the study. Verbal working memory span was assessed by means of the letter-number span. The Digit Copy test was used to assess motor speed, and the Digit Symbol Substitution Test to assess cognitive speed.


RESULTS
The working memory span was significantly impaired in patients (F(1,90)=4.6, P<0.05). However, the group difference was eliminated when either the motor or the cognitive speed measure was controlled (F(1,89)=0.03, P=0.86, and F(1,89)=0.03, P=0.88). In the patient group, working memory span was significantly correlated with negative symptoms (r=-0.52, P<0.0001) and thought disorganisation (r=-0.34, P<0.025) scores. Regression analyses showed that the association with negative symptoms was no longer significant when the motor speed measure was controlled (β=-0.12, P=0.20), while the association with thought disorganisation was no longer significant when the cognitive speed measure was controlled (β=-0.10, P=0.26).


CONCLUSIONS
Decrement in motor and cognitive speed plays a significant role in both the verbal working memory impairment observed in patients and the associations between verbal working memory impairment and clinical symptoms.
Unit of Research and Development, Parc Sanitari Sant Joan de Déu (PSSJD), CIBERSAM, C/Doctor Antoni Pujadas 42, 08830 Sant Boi de Llobregat, Barcelona, Spain. Electronic address: gildas.brebion@pssjd.org.
G
G
Brébion
Unit of Research and Development, Parc Sanitari Sant Joan de Déu (PSSJD), CIBERSAM, C/Doctor Antoni Pujadas 42, 08830 Sant Boi de Llobregat, Barcelona, Spain.
C
C
Stephan-Otto
Unit of Research and Development, Parc Sanitari Sant Joan de Déu (PSSJD), CIBERSAM, C/Doctor Antoni Pujadas 42, 08830 Sant Boi de Llobregat, Barcelona, Spain.
E
E
Huerta-Ramos
Unit of Research and Development, Parc Sanitari Sant Joan de Déu (PSSJD), CIBERSAM, C/Doctor Antoni Pujadas 42, 08830 Sant Boi de Llobregat, Barcelona, Spain.
J
J
Usall
Unit of Research and Development, Parc Sanitari Sant Joan de Déu (PSSJD), CIBERSAM, C/Doctor Antoni Pujadas 42, 08830 Sant Boi de Llobregat, Barcelona, Spain.
M
M
Perez Del Olmo
Unit of Research and Development, Parc Sanitari Sant Joan de Déu (PSSJD), CIBERSAM, C/Doctor Antoni Pujadas 42, 08830 Sant Boi de Llobregat, Barcelona, Spain.
M
M
Contel
Unit of Research and Development, Parc Sanitari Sant Joan de Déu (PSSJD), CIBERSAM, C/Doctor Antoni Pujadas 42, 08830 Sant Boi de Llobregat, Barcelona, Spain.
J M
JM
Haro
Unit of Research and Development, Parc Sanitari Sant Joan de Déu (PSSJD), CIBERSAM, C/Doctor Antoni Pujadas 42, 08830 Sant Boi de Llobregat, Barcelona, Spain.
S
S
Ochoa
D016022:Case-Control Studies; D003071:Cognition; D005260:Female; D006801:Humans; D008297:Male; D008570:Memory, Short-Term; D008875:Middle Aged; D009483:Neuropsychological Tests; D011581:Psychological Tests; D011597:Psychomotor Performance; D012565:Schizophrenic Psychology; D013997:Time Factors
Negative symptoms; Processing speed; Schizophrenia; Thought disorganisation; Working memory