Abstract
Attending and responding to sound location generates increased activity in parietal cortex which may index auditory spatial working memory and/or goal-directed action. Here, we used an n-back task (Experiment 1) and an adaptation paradigm (Experiment 2) to distinguish memory-related activity from that associated with goal-directed action. In Experiment 1, participants indicated, in separate blocks of trials, whether the incoming stimulus was presented at the same location as in the previous trial (1-back) or two trials ago (2-back). Prior to a block of trials, participants were told to use their left or right index finger. Accuracy and reaction times were worse for the 2-back than for the 1-back condition. The analysis of functional magnetic resonance imaging data revealed greater sustained task-related activity in the inferior parietal lobule (IPL) and superior frontal sulcus during 2-back than 1-back after accounting for response-related activity elicited by the targets. Target detection and response execution were also associated with enhanced activity in the IPL bilaterally, though the activation was anterior to that associated with sustained task-related activity. In Experiment 2, we used an event-related design in which participants listened (no response required) to trials that comprised four sounds presented either at the same location or at four different locations. We found larger IPL activation for changes in sound location than for sounds presented at the same location. The IPL activation overlapped with that observed during the auditory spatial working memory task. Together, these results provide converging evidence supporting the role of parietal cortex in auditory spatial working memory which can be dissociated from response selection and execution.
Highlights
Evidence from neuroanatomical and neurophysiological studies in non-human primates (e.g., Romanski et al, 1999; Poremba et al, 2003) as well as neuroimaging studies in humans (e.g., Alain et al, 2001; Maeder et al, 2001) suggest that auditory cognition depends on at least two functionally distinct pathways
Some authors have proposed that the dorsal pathway supports processes involved in localizing and remembering sound location (e.g., Alain et al, 2001, 2008; Maeder et al, 2001; Arnott et al, 2004, 2005; Rama et al, 2004; Deouell et al, 2007) as well as other sound attributes that could be spatially encoded in sensory memory such as pitch, motion, and loudness (McLachlan and Wilson, 2010)
FMRI results Figure 1 shows the results of the mixed model analysis used to separate sustained task-related and transient target-related activity
Summary
Evidence from neuroanatomical and neurophysiological studies in non-human primates (e.g., Romanski et al, 1999; Poremba et al, 2003) as well as neuroimaging studies in humans (e.g., Alain et al, 2001; Maeder et al, 2001) suggest that auditory cognition depends on at least two functionally distinct pathways. Others have recast the dorsal stream as a pathway critical for sensory-motor integration and goal-directed action (Hickok and Poeppel, 2000; Zatorre et al, 2002; Warren et al, 2005) akin to the perceptionaction model of visual scene analysis (Goodale, 2008) These theoretical accounts are not mutually exclusive and suggest that multiple functions may be supported by the dorsal streams during auditory scene analysis. Responding to infrequent targets was associated with enhanced signal in the left pre- and post-central gyrus, prefrontal cortex and bilateral IPL These results are consistent with a dual role for the parietal cortex in auditory scene analysis – one involved in representation of auditory space and another that underlies auditory motor transformation (Alain et al, 2008). As neither working memory load nor response demand were manipulated in that study, it remains unclear www.frontiersin.org
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