Reviews and perspectivesLeft ventrolateral prefrontal cortex and the cognitive control of memory
Introduction
Whether determining the appropriate utensil to use at a formal dinner, how much money is necessary for a trip on the subway, or the right words to use when greeting a long absent friend, memory informs our behavior. Sometimes knowledge relevant to our goals comes to mind automatically, in a bottom-up fashion, simply by processing cues in our environment. Often, however, relevant experiences from the past or facts about the world do not readily come to mind. In these instances, we must search memory strategically and focus attention on relevant retrieved information. Cognitive control mechanisms, supported by the prefrontal cortex (PFC), allow us to be strategic in making memory subject to our intents and needs. Hence, the cognitive control of memory is fundamental to flexible, goal-directed behavior.
In this review, we focus on the contribution of left ventrolateral prefrontal cortex (VLPFC) to the control of memory. VLPFC encompasses the inferior frontal gyrus anterior to premotor cortex (Brodmann's area [BA] 6) and posterior to the frontal pole (BA 10), and consists of three gross anatomical subdivisions: pars opercularis, pars triangularis, and pars orbitalis. Respectively, these subdivisions correspond approximately to BA 44, BA 45, and the portion of BA 47 along the inferior frontal gyrus, not including caudal orbital frontal cortex. This latter subdivision maps to what Petrides and Pandya (2002b) term area 47/12, noting the homology between area 47 in the human and area 12 in the macaque monkey (Fig. 1).
Functional examination of left VLPFC holds a prominent place in the history of neuropsychology, dating back to Paul Broca's work on non-fluent aphasia (Broca, 1861). More recently, convergent data from a variety of methodologies have highlighted a broader role for VLPFC beyond strict language production (Badre & Wagner, 2002; Buckner, Raichle, & Petersen, 1995; Gabrieli, Poldrack, & Desmond, 1998; Petersen, Fox, Posner, Mintun, & Raichle, 1988; Petrides, 2000; Poldrack & Wagner, 2004; Thompson-Schill, 2003; Thompson-Schill, Bedny, & Goldberg, 2005; Wagner, 1999). In particular, neuropsychological and neuroimaging data have linked left VLPFC with the cognitive control of memory (Badre, Poldrack, Paré-Blagoev, Insler, & Wagner, 2005; Buckner, 1996, Gabrieli et al., 1998, Petrides, 2002; Thompson-Schill, D’Esposito, Aguirre, & Farah, 1997; Wagner, Paré-Blagoev, Clark, & Poldrack, 2001). Initial evidence pointed to a fractionation within VLPFC according to representational content (i.e., the semantic-phonological hypothesis; e.g., Buckner et al., 1995, Fiez, 1997, Poldrack et al., 1999; Price, Wise, & Frackowiak, 1996). However, as evidence has accumulated, it has become increasingly apparent that anatomically distinct subcomponents of left VLPFC also can be distinguished based on their association with distinct forms of cognitive control. In this review, we consider this more recent evidence for dissociable control processes within left VLPFC, and illustrate how these processes impact behavior across a range of different task domains in which access to memory is critical.
Section snippets
Left VLPFC and semantic retrieval
Semantic memory consists of long-term knowledge of facts, word meanings, and object properties (Tulving, 1972). Semantic knowledge is represented in a distributed manner (McClelland & Rogers, 2003), and its storage and retrieval partially depend on inferior and lateral temporal cortical regions (Damasio, 1990; Damasio, Tranel, Grabowski, Adolphs, & Damasio, 2004; Farah & McClelland, 1991; Gorno-Tempini et al., 2004; Martin & Chao, 2001; Nobre, Allison, & McCarthy, 1994; Thompson-Schill, 2003).
VLPFC and episodic retrieval
Episodic memory supports conscious remembrance of life events, providing a record of past experiences that, when retrieved, can inform current decision and action (Tulving, 1972, Tulving, 2002). Broadly defined, episodic memory allows an organism to discriminate between familiar (encountered) and novel stimuli, and to recollect specific event details surrounding a prior encounter with a stimulus (Cohen, Eichenbaum, & Poldrack, 1997; Squire, 1992). Of particular interest for present purposes is
Post-retrieval selection and proactive interference in working memory
Post-retrieval selection is critical when competition is present due to simultaneously active representations. One fundamental form of competition in memory is proactive interference (PI), wherein previous processing (and concomitant representations) negatively influence subsequent processing. Behaviorally, PI leads to slowing and can cause forgetting over long and short intervals (e.g., Anderson & Neely, 1996; Brown, 1958; Keppel & Underwood, 1962; Mensink & Raaijmakers, 1988). At least some
Task-switching, proactive interference, and post-retrieval selection
The ability to strategically access memory is critical for flexible behavior. For example, consider being interrupted, while writing a manuscript, by a phone call from a friend who wants to meet you for dinner in the evening. Previously relevant information, such as what references to include in your introduction, must now give way to a new set of relevant information, such as good restaurants that are close to your friend's home. Given that this newly relevant information must be retrieved,
Beyond retrieval and selection
Though we view the two-process model to be a parsimonious account of the role of left anterior and mid-VLPFC across a range of tasks requiring the cognitive control of memory, considerable work remains to formally specify these neural mechanisms and to more fully comprehend their broader role in cognition. In this final section, we consider how the two-process model relates to other accounts of left VLPFC function, and highlight open avenues for future research.
Conclusion
The cognitive control of memory permits an organism to strategically bring knowledge to bear on behavior, enabling flexible cognition and action. In this review, we have considered evidence for two cognitive control mechanisms – controlled retrieval and post-retrieval selection – that are supported by left anterior and mid-VLPFC, respectively. These mechanisms appear critical for mnemonic control across several task domains.
While we believe that the two-process model constitutes meaningful
Acknowledgements
Supported by the NSF (BCS-0401641), NIMH (R01-MH080309-01) the McKnight Endowment Fund for Neuroscience, and the Alfred P. Sloan Foundation. We thank Brian Gold and Ian Dobbins for provision of data figures.
References (175)
- et al.
Remembering the past and imaging the future: Common and distinct neural substrates during event construction and elaboration
Neuropsychologia
(2007) - et al.
Interference and inhibition inmemory retrieval
- et al.
Inhibition and the right inferior frontal cortex
Trends in Cognitive Sciences
(2004) - et al.
Dissociable controlled retrieval and generalized selection mechanisms in ventrolateral prefrontal cortex
Neuron
(2005) - et al.
Selection, integration, and conflict monitoring; assessing the nature and generality of prefrontal cognitive control mechanisms
Neuron
(2004) - et al.
Cortical mechanisms specific to explicit visual object recognition
Neuron
(2001) - et al.
Functional interactions of the inferior frontal cortex during the processing of words and word-like stimuli
Neuron
(2001) - et al.
The role of the inferior frontal junction area in cognitive control
Trends in Cognitive Sciences
(2005) - et al.
Neural mechanisms of transient and sustained cognitive control during task switching
Neuron
(2003) Frontally mediated control processes contribute to source memory retrieval
Neuron
(2002)