Delay tasks (delayed response and delayed non-matching to sample)
Imported into the somatic marker programme from the non-human primate working-memory literature, for one purpose: to show that the VM patients who fail the iowa-gambling-task are not failing it because they cannot hold information in mind.
Enters this wiki with Bechara, Damasio & Damasio (2000), where the result is reported in full. The wiki had carried it only as a line on antoine-bechara (“dissociated working memory from decision-making within human prefrontal cortex”).
Why it exists
The somatic-marker-hypothesis needs the VM patient to be specifically impaired. If the same lesion degraded working memory, the gambling deficit would be explicable without any appeal to bodily signals — you cannot weigh long-run consequences you cannot hold onto. Conventional testing already showed normal IQ, language and attention, but “working memory” as measured in the primate tradition is a sharper instrument aimed at the neighbouring cortex, and the dorsolateral sector is precisely where the frontal-lobe literature had located it (Goldman-Rakic; Fuster; Milner and Petrides).
So the design is a crossing: two frontal lesion groups, two tasks, one prediction each.
| delay tasks | gambling task | |
|---|---|---|
| bilateral anterior VM (n = 9) | normal — some superior | severely impaired |
| right dorsolateral (n = 10, right-lesioned subset) | impaired | low-normal |
| left dorsolateral | normal | — |
The asymmetry, which is the part worth keeping
Cited as a double dissociation, and anatomically it is one. Functionally it is not symmetric, and the source says so plainly: “working memory and decision making were asymmetrically dependent.”
- Working memory does not need decision-making. A VM patient can be at floor on the gambling task and at ceiling on the delay tasks.
- Decision-making partly needs working memory. Right-DL patients with severe delay-task impairment did not choose badly — they chose advantageously, but their gambling performance “falls in the low normal range.”
This matters for how the wiki reads a specific criticism. iowa-gambling-task lists working memory as the first of five rival explanations of the VM deficit catalogued by Dunn et al. (2006). The Iowa group had already measured it, five years earlier, and found it a partial contributor rather than a substitute explanation. What the design does not do — and what would be needed to retire the rival — is quantify how much of the VM deficit survives after working memory is accounted for. Nine patients, no statistics, no covariate analysis.
It also sits with the second Dunn revision on ventromedial-prefrontal-cortex: IGT performance is worse with damage extending into DLPFC (Bechara et al. 1998b — the same study), correlates with DLPFC resting-state activity, and large PFC lesions impair the task where discrete ones may not. The framework absorbs this by saying markers work partly through attention and working-memory allocation, at the cost Dunn et al. name: it “does make the predictions of the SMH difficult to distinguish from other, non-somatic theories.” The delay tasks are where that cost was first incurred, by the framework’s own authors, reporting it as a finding.
The anatomical byproduct
The more durable result may be the one about lesion extent rather than about working memory. All nine VM patients failed the gambling task, but they split on the delay tasks — and the split tracked anatomy:
- Abnormal gambling / abnormal delay (n = 5): lesions extending posteriorly, plausibly into the basal forebrain.
- Abnormal gambling / normal delay (n = 4): lesions confined anteriorly, sparing it.
Posterior extension toward basal forebrain is the same variable that predicts the other co-morbid deficits in this material — ventromedial-prefrontal-cortex records Tranel et al. (1996), where patients with lesions reaching ACC and basal forebrain fail Pavlovian conditioning as well as gambling, and the 2000 paper separately notes that VM patients with basal-forebrain involvement do show motor impulsiveness and perseveration where anterior-only patients do not.
So “the VM patient” is at least two patients, and which one you have is legible from the posterior margin of the lesion. That is a caution about every group-level VM result in this wiki, and it is available from the Iowa material itself.