Functional Organization of Primary Somatosensory Cortex Depends on the Focus of Attention

Abstract

We used magnetic source imaging in human subjects to reveal within-subject variations of the homuncular hand representation within the primary somatosensory cortex modulated by attention. In one condition subjects were trained to detect sequential leftward or rightward stimulus motion across the fingers of the left hand ("hand" condition) and in a different condition to detect stimulus motion at a specific finger on this hand ("finger" condition). Afferent input was controlled by applying exactly the same stimulus pattern to the digits in the two tasks. Segregation of the somatotopic hand representation (an increase in the distance between the representations of digits 2 and 5) was observed, commencing with the onset of practice, in the finger relative to the hand condition. Subsequent training in the hand and finger conditions with feedback for correctness did not modify segregation, indicating that segregation was a task effect and not a training effect. These findings indicate that the hand representation within the primary somatosensory cortex is not statically fixed but is dynamically modulated by top-down mechanisms to support task requirements. A greater capacity for modulation of the functional cortical organization was positively correlated with superior learning and task performance.

Neural Correlates of Tactile Detection: A Combined Magnetoencephalography and Biophysically Based Computational Modeling Study

“…The mean differences show that the stimulus amplitude differences were not driven by the response of an outlier subject. SI, consistent with other studies of tactile stimulation to the fingers (Forss et al, 1994b;Hoechstetter et al, 2000Hoechstetter et al, , 2001Kakigi et al, 2000;Braun et al, 2002;Druschky et al, 2003;Iguchi et al, 2005). Figure 1 shows representative examples of the location and orientation of the ECD on T1-weighted MRI images.…”

Tactile acuity in experienced Tai Chi practitioners: evidence for use dependent plasticity as an effect of sensory-attentional training

“…The specific measure studied here, tactile spatial acuity at the fingertip, is correlated with cortical measures [see especially, remodeling of primary sensory maps as reported by Hodzic and colleagues (2004) and by Sathian and colleagues (2002)]. More generally, it is known that short-term attentional focus on the fingers facilitates changes in S1 cortical somatotopic map (Braun et al, 2002;Noppeney, Waberski, Gobbele, & Buchner, 1999). A positive finding would suggest that practitioners' long-term focus of a specific attentional "spotlight" on the fingertips increases the gain of neuronal responses (e.g., amplifies the attended inputs) and evokes cortical remodeling in early sensory maps.…”

Attentional Modulation of Spatial Integration of Pain: Evidence for Dynamic Spatial Tuning

“…Across different modalities such as vision (Salinas and Abbott, 1997), audition (King et al, 2007), and somatosensation (Faggin et al, 1997), one way to better adapt the nervous system to various situations is by dynamically modulating how information is processed. Central plasticity of sensory maps can be implemented by bottom-up (Pleger et al, 2001) or top-down mechanisms (Braun et al, 2002) that are activated in contextdependent fashions according to the circumstances of the environment or cognitive demands. Rapid and reversible plasticity in the somatosensory system has been reported (Stavrinou et al, 2006) in the dorsal horn (Hayes et al, 1981), dorsal column nuclei (Pettit and Schwark, 1993), brainstem (Faggin et al, 1997), thalamus (Faggin et al, 1997), and cortex (Faggin et al, 1997).…”

“…RF tuning can be modulated by CNS circuits that convey information about training and/or attentional requirements (Gilbert, 1998). This top-down modulation can select higher-order representations of lower-level sensory features that better fit in a single event/task (polymaps) (Swindale et al, 2000), using short-term neuroplastic mechanisms activated by attention (Braun et al, 2002).…”

“…Task dependent tuning of receptive fields is found across visual (McAdams and Maunsell, 1999), auditory (Ahveninen et al, 2006), and somatosensory (Hayes et al, 1981) systems. Such tuning is associated with altered perceptual experiences as indicated by more frequent and more accurate detection of stimuli (Braun et al, 2002;Quraishi et al, 2006). Attention may be a modulatory factor that produces dynamic alterations of the receptor field sizes of wide dynamic range and nociceptive specific neurons.…”