Corsi Block Tapping Task

The CBT task (Corsi, 1972) is a neuropsychological test of visuo-spatial working memory (VSWM). The test involves copying an experimenter after they tap a series of blocks in a specific order. There are 9 blocks that are identical in appearance. In its standard form the experimenter usually begins by touching 2 blocks (encoding phase), with the participants having to reproduce the series of block taps (response phase) in the same sequence (‘forward’ task) or in reverse order (‘backward’ task). If a certain proportion of the blocks are tapped in the correct order (usually 1/2, 2/3, or 3/5 of the trials per sequence length) then the experimenter will increase the sequence length by 1 block at a time. Performance

on the CBT task reduces as participants are required to remember more block locations in a sequence that is not perceived to be meaningful (Toepper et al., 2010). When the number of incorrect reproductions exceeds a certain proportion the test stops. The Corsi span averages 5 in normal adult subjects (Kessel et al., 2000). Performance on the CBT task can be measured in terms of the proportion of correct responses, as well as the reaction time of correct responses (Toepper et al., 2010).

Berch et al. (1998) described the CBT task as the most important non-verbal task in neuropsychological research. As well as being widely used in diagnostics for assessing VSWM, the CBT task also measures spatial attention (Smyth and Scholey, 1994). The CBT task is often used as part of test batteries to diagnose diseases such as Alzheimer's disease (Carlesimo et al., 1996), Korsakoff's syndrome (Haxby et al., 1983), schizophrenia (Chey et al., 2002), as well as helping to localise focal brain lesions (Milner, 1971). The CBT is also widely used in research as a measure of VSWM (Fischer, 2001; Bo et al., 2011).

VSWM is a neuropsychological concept, which underlies the ability to store, maintain and manipulate spatial information (Toepper et al., 2010). VSWM has mainly been viewed in regards to the working memory model of Baddeley and Hitch (1974,1986). This model consists of two components: the visuospatial sketchpad and the central executive. The visuospatial sketchpad is responsible for the storage of object-related and spatial information and associated with right-sided or bilateral parietal brain regions (Kessels et al., 2000). The central executive is responsible higher-level cognitive operations. These can be divided into different sub-functions (e.g. manipulation and updating information, dual task coordination, and inhibition (Collette and Van der Linden, 2002)).

Lesion studies have revealed that damage to the frontal lobes results in relatively poor performance on the CBT task. Damage to the PFC, in particular the right DLPFC, is associated with deficits in spatial span (van Asselen et al., 2006; Bor et al., 2006; TeixeiraFerreira et al., 1998). Bor et al. (2006) analysed performance on spatial span tasks (similar to the CBT) in individuals with frontal lesions. The results revealed that the individuals with frontal lobe lesions were significantly impaired on the CBT. Those with lesions to the right DLPFC were particularly impaired. van Asselen et al. (2006) had individuals with brain lesions complete the CBT. Damage to the right DLPFC and the right posterior parietal

cortex was found to impair performance on the CBT. These individuals struggled to maintain spatial information over extended periods of time, indicating the importance of these areas for spatial working memory. Kessels et al. (2000) carried out a meta-analysis on the effects that lesions had on performance on spatial span tasks (similar to the CBT). They found that individuals with frontal lobe lesions performed worst on the task through having the lowest Corsi spans.

Their performance was worse than that of individuals who had undergone temporal lobectomies.

Bor et al. (2001) used PET to analyse neural activity during spatial span tasks (similar to the CBT). The results revealed increased activity in the DLPFC as well as the VLPFC during the task. The authors concluded that these areas are involved spatial working memory. Owen et al. (1996) had participants complete the CBT while they underwent PET imaging. The results showed that the CBT elicited activity in the PFC, primarily in the VLPFC.

An adaptation of the CBT task is the Block Suppression Task (BST) that is thought to require spatial inhibition as a key component to the task (Beblo et al., 2004). As mentioned in Chapter 4, inhibition is an executive function that is heavily associated with areas such as the DLPFC. The BST test an individual’s ability to ignore irrelevant spatial information during the CBT and only attend and respond to the target blocks in a sequence. The BST has been tested on individuals Alzheimer’s disease. Toepper et al. (2008) reported that the individuals with Alzheimer’s were specifically impaired on the BST compared to healthy controls.

This indicated that the BST was an appropriate task for differentiating between those with Alzheimer’s and those who do not have it, meaning that the BST may be a useful tool for diagnosing those with neurological disorders that affect the inhibitory functions of the PFC.

Toepper et al. (2010) carried out an fMRI study using both the CBT task and the BST to investigate the neural substrates responsible for the maintenance of short-term spatial information (for the CBT task) as well as the inhibition of spatial information (for the BST). Behavioural results revealed that correct responses were fewer and reaction times were longer for the CBT in comparison to the BST.

fMRI results revealed that during the encoding phase of the CBT task there was increased activity in the right DLPFC and VLPFC. During the encoding phase of the BST there was increased activity in the left DLPFC. These findings

demonstrate that encoding of spatial information and the inhibition of spatial information recruit different areas of the PFC.

The authors argued that these results supported a process-specific fractionated model of spatial working memory in the PFC. They proposed that the encoding of visuo-spatial information recruits the VLPFC and the DLPFC (as used in the CBT), whereas higher executive functions are associated with the DLPFC.

The authors stated that the results suggest that the left DLPFC is involved in inhibiting spatial distraction during working memory processes. This is supported by research that has indicated that frontal activity reflects inhibitory functions that prevent distractors from interfering with working memory (Vogel and Machizawa, 2004). The fMRI results also indicated that parietal activity was correlated with working memory load. The BST therefore provides a further means of investigating PFC haemodynamic activity using fNIR.