Table 1.

Comparison of six major parameters across several microinjectrode systems. The parameters listed in the first column are among the most relevant for successful long-term, reliable microinjection, and single-neuron recordings in behaving monkeys. A single plus in the row 1 indicates systems in which volume monitoring is accomplished only at the infusion pump stage, whereas two pluses represent systems in which the monitoring is also accomplished after the pump stage and closer to the infusion cannula. A single plus in row 2 indicates systems that use microwires for recording, whereas two pluses indicate systems using conventional electrodes with etched, tapered tips. Single pluses in row 4 indicate systems in which guide tubes (21G–25G) or pre-puncturing of the dura is needed for insertion of the microinjectrode; two pluses indicate that the microelectrode is protected by the small diameter (32G) infusion cannula. Pluses in row 5 indicate systems incorporating a proactive means of preventing the clogging of the cannula. The parameter in row 6 refers to the absolute distance between the microelectrode tip and the presumed center of the drug delivery volume. Columns marked “high” are systems in which the microelectrode and the injection cannula are attached side-by-side; all other systems employ coaxial arrangements.

microinjection system	Crist, Yamasaki, Komatsu, and Wurtz, 1988	Dias and Segraves, 1997	Tokuno, Ikeuchi, et al., 1998	Martin and Ghez, 1999	Chen, Goffart and Sparks, 2001	Kliem, Wichmann, 2004	Noudoost and Moore, 2010
important parameters
1) Fluid volume monitoring	+	++	+	++	+	+	++
2) Recording quality	+	+	+	+	++	++	++
3) Maximum diameter inside the brain (μm)	305	305	311+75	200	229	250+103	236
4) Microelectrode protection during dura-brain penetration	+	+	+	+	+	+	++
5) Clog prevention	–	–	–	–	–	+	+
6) Offset between infused drug and microelectrode	low	low	high	low	low	high	low