Premotor Cortex & SMA

Anatomy

• BA 6: premotor cortex (PMC) laterally, supplementary motor area (SMA) on the medial surface, and pre-SMA in front of it.
• The frontal eye field (FEF) lies within BA 8, in front of the premotor cortex.
• Immediately anterior to the primary motor cortex; also sends fibers to the corticospinal tract.
• Blood supply: lateral part MCA, medial SMA ACA.

Functions

• Planning and preparing movement; movement guided by external cues (lateral PMC).
• Internally initiated and sequential movements (SMA).
• Bimanual coordination and motor learning.
• Action understanding and imitation (ventral PMC — mirror neuron system).
• Pre-SMA: response selection and inhibition.
• FEF: voluntary saccades and orienting of visual attention.

Connections and chemistry

• Primary motor cortex
• Putamen (motor loop)
• Thalamus — VA/VL nuclei
• Cerebellum (dentate → thalamus → cortex)
• Posterior parietal cortex (visuomotor transformation)

Development

Developmental course through childhood and adolescence.

• Fine motor skills and sequence learning develop rapidly in the school years.
• Mirror movements normally decrease markedly by about age 10; linked to maturation of the corpus callosum.

Clinical

• Tourette syndrome and chronic tic disorders: SMA hyperactivity, part of the premonitory urge network.
• Developmental coordination disorder (DCD): difficulty with motor planning.
• ADHD: increased mirror movements, differences in motor inhibition.
• ASD: differences in imitation and motor planning (dyspraxia).

Treatment

This region from the perspective of medication, psychotherapy and neuromodulation. Letter badges are evidence levels.

• Developmental coordination disorder: task-oriented approaches (practicing directly the skill the child struggles with in daily life; e.g. CO-OP, neuromotor task training) and motor-based interventions; the mean effect in meta-analysis is large (d ≈ 1.06) but study quality is limited (Smits-Engelsman et al., 2018). B
• Premonitory urge (SMA and insula): CBIT teaches awareness of the urge and a competing response; details on the putamen card. A
• ADHD and DCD often co-occur; motor difficulties affect handwriting and participation in sports, calling for occupational therapy and school accommodations.

Assessment

Neuropsychological tasks and measures that probe this region's function.

• Luria motor sequence (fist–edge–palm)
• Sequential finger tapping, Purdue Pegboard
• Antisaccade task (FEF)
• Praxis assessment, neurological soft signs (PANESS)

Lesions and damage

Clinical findings expected with damage or dysfunction.

• SMA syndrome: reduced initiation of voluntary movement and speech (transient akinesia).
• Alien hand syndrome (medial frontal), ideomotor apraxia.
• FEF lesion: contralateral saccade impairment, gaze deviation toward the side of the lesion.

In the model

How this structure is defined in the 3D model, and the data source.

HCP-MMP1.0 areas (Glasser et al., 2016; MNI volumetric version: Horn, 2016): 6a, 6d, 6v, 6r, 55b, FEF, PEF (lateral premotor) and 6ma, 6mp, SCEF (SMA and pre-SMA, medial surface).

References

Full citations for the card; links go to the paper (DOI) or a PubMed search.

1. Smits-Engelsman B et al. Evaluating the evidence for motor-based interventions in developmental coordination disorder: a systematic review and meta-analysis. Res Dev Disabil 2018. Search PubMed