# Recent Advances in Myoelectric Control for Finger Prostheses for Multiple Finger Loss
## 3 Signals and Finger Motor Function  
Signals are important for the control of the myoelectrical (prosthetic) hands or fingers. Figure 1 shows a myoelectrically controlled hand prosthesis (designed in computer software), a design to collect EMG signals, and the generated signals [14]. The motor and sensory components of the hand provide an individual with high functionality and elegant behavior through a complex integrated system [15]. Human hands can perform numerous actions, varying from handling heavy objects to fine digital movements while directly connecting with the brain. It would ideal if similar movements can be performed by prosthetic hands and fingers. An intelligent interface that controls prosthetic hands and fingers can suggest movement by interpreting a muscle's electrical activity via the surface EMG signal [16; 17]. Figure 2 shows a myoelectrically controlled hand prosthesis, the generation of signals, and EMG channels [6]. The myoelectric activities of the residual limb for the phantom limb movements (PLM) may help for pattern recognition in the context of myoelectrical control [17]. Finger movements require specific stimulation of a group of muscles [18]. Such stimulation is principally controlled by the motor cortex through the corticospinal tract. The motor cortex's output operates via corticospinal projection, which is important for the movements of the finger. Normally, an action potential propagates and activates a motor neuron which in turn activates the muscle fibers. When the depolarization of the postsynaptic membrane of muscle fiber takes place, the depolarization spreads along the fiber supplemented by the movement of ions and generates an electromagnetic field [19]. Myoelectric or EMG signals are read by microelectrodes and the signals are amplified, from which the muscle's naturally generated electricity can be measured [16]. The signals are assigned to control the movement of the prosthesis after processing. Specific EMG pulse sequences are linked to a specific movement of the prosthesis. The predefined movements are controlled by specific signals [20]. Figure 1: Myoelectrically controlled hand prosthesis designed in computer software, a design to collect the electromyography (EMG) signals, and sample generated signals [14]. Figure 2: Active myoelectrically controlled hand prosthesis, generation of signals, and signals in the electromyography (EMG) [10]. The effectiveness of prosthetic hands can be assessed by user performance when performing functional tasks. [PERSON] et al. [21] compared the upper limb activity between myoelectric prosthesis users and normal adults and found that temporal patterns in upper limb activity were present. It was also found that prosthesis users were greatly reliant on their intact limbs for daily activities. There was no significant correlation between the kinematic and the gaze-related performance between myoelectric prosthesis users and normal adults. Access to the neural control information for an arm is lost during amputation. Hence, improving the function of hands or finger prosthesis poses a challenge. Various invasive methods have been proposed to generate proper signals for myoelectrical prostheses, such as peripheral nerve signal transmission [22], motor cortex [23], or targeted muscle reinnervation (TMR) [24] methods. In TMR, the muscle of the amputee is reinnervated with the residual nerves of the amputated limb. Following the reinnervation, the target muscles produce EMG signals, and these signals can control the prosthetic hand/arm and have promising results [25]. [PERSON] et al. [26] studied four types of control for a prosthetic hand (TMR, myoelectric, cortical interfaces, and peripheral nerve interfaces) in upper-limb amputees and found that the participants showed a maximum positive response for the myoelectrical interface, while they showed the least interest for the cortical interface. More skillful individual and combined finger control has not yet been gained [27]. [PERSON] et al.