Figure 1.
Details of the experiment of Fogassi et al. [14].
(a) Lateral view of the monkey brain showing the sector of IPL (dark shading) from which the neurons were recorded. (b) The apparatus and the paradigm used for the motor task. I. grasping for eating. II. and III. grasping for placing inside a container put near the mouth or near the target, respectively. (c) Activity of two IPL neurons during the two grasping conditions. Rasters and histograms are aligned with the moment when the monkey touched the object to be grasped. x axis, time, bin 20 ms; y axis, discharge frequency (spikes per second).
Figure 2.
Differential discharge of a mirror neuron during the motor and the visual task.
Rasters and histograms are synchronized with the moment when the monkey or the experimenter touched the object to be grasped. Other conventions as in figure 1.
Figure 3.
Schematic representation of three connected neuronal pools.
Inhibitory neurons are represented as darker elements while excitatory neurons are represented as lighter elements.
Figure 4.
Time course of the activity (rasters and histograms) of 4 neurons recorded in IPL.
Each one codes a specific motor act, but is active only when the monkey executes the “grasping to eat” sequence. Both rasters and histograms are aligned with the moment in which the monkey touches the object. Beneath the histograms a schematic representation of the corresponding neuronal chain is shown.
Figure 5.
Connection scheme for one neuronal chain. Each colored circle represents a pool of neurons that codes a specific motor act.
Pre-frontal input triggers the activation of the chain, while sensory and motor signals modulate the propagation of the activity within the chain. This scheme shows the path of the motor commands (from IPL to PMC to M1) and of the efferent copies (from M1 to PM to IPL). Sensory information (dashed line), which results from the interaction of the individual with the environment, follows an indirect route through sensory areas. M1 = primary motor cortex; PMC = premotor cortex; PFC = prefrontal cortex.
Figure 6.
Schematic representation of the areas and the populations of neurons that are active during the motor task.
The prefrontal cortex contains the motor intentions (in the figure: mot. intent.) and thus acts as the chain selector, while sensory and motor corollary signals regulate the transmission of activity waves within the chains.
Figure 7.
Representation of the time course of the activity patterns of four neurons of the simulated chain.
The colored histograms represent the activity of neurons coding different motor acts: the green peak represents “reaching”, the red “shaping”, the blue “grasping” and the magenta “bringing to the mouth”. Both rasters and histograms are aligned with the moment () in which the simulated monkey touches the object.
Figure 8.
Representation of the activity of the pools forming the “reaching to place” chain during a “reaching to eat” task.
The color indicates the neuronal activity related to the type of motor act (green = “reaching”, red = “shaping”, blue = “grasping”, orange = “placing”). Both rasters and histograms are aligned with the moment () in which the simulated monkey touches the object.
Figure 9.
Schematic representation of the areas and the population of neurons that are active during the visual task.
Figure 10.
Representation of the responses of 4 neurons of the network at different moments of the learning phase.
Panel A) response in the initial configuration; B) after 150 sessions; C) after 250 sessions; D) after 500 sessions. Color code as in Figure 4.
Figure 11.
Schematic representation of two connected neuronal pools.
Inhibitory neurons are represented as darker elements while excitatory neurons are represented as lighter elements. Arrows and the corresponding neurotransmitter indicate the type of connections between neurons within and outside the pool.
Figure 12.
Representation of a pool's response as function of the excitatory and the inhibitory connections' strength.
Different colors represent different levels of activity. The black area represents the combination of parameters that leads to a non-transient response of the pool. The white circle indicates the values of the connections' strength chosen in the simulations.