It was possible to demonstrate by other methods refined structural differences among neuron types ; however, proof was lacking that the quality of the impulse or its condition was influenced by these differences , which seemed instead to influence the developmental patterning of the neural circuits .

　　有可能通过其他方法来证明神经元种类间的细微的结构差异;可是，这样的证据是缺乏的，即神经冲动的性质或者状态是受这些差异所影响的，而这些差异看起来却能影响神经网络的发育模式。

　　难句类型：复杂修饰、倒装

　　解释：与很多人的印象相反，lack从来就不能作形容词，它只有动词或名词的词性。其形容词的形式是lacking,意思是缺乏的、不足的。

　　本句的在however 之前和之后的两个分句，是两个倒装结构，前一个是小倒装，正常语序是：to demonstrate refined structural differences among neuron types by other methods: however后面是个大倒装，lacking之后的that引导的同位语人名是修饰主语proof的，但是因为它太长，所以为了避免头重脚轻，被放到lacking之后，正常的语序应该是proof that the quality of ..was lacking

　　训练：It was possible to demonstrate by other methods refined structural differences among neuron types; however, proof was lacking that the quality of the impulse or its condition was influenced by these differences, which seemed instead to influence the developmental patterning of the neural circuits.